JP2011143462A - Method for manufacturing thick steel plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a time-saving efficient method for manufacturing a thick steel plate when manufacturing the thick steel plate by rolling. <P>SOLUTION: The method for manufacturing the thick steel plate includes: a preceding rolling step for hot-rolling the steel plate 3 by a reversible rolling mill 7 to have a controlled rolling start plate thickness at a controlled rolling start temperature; and a controlled rolling step for carrying out controlled rolling while controlling temperature or the like after the preceding rolling step. The preceding rolling step includes an inter-pass water-cooling step for water-cooling the steel plate 3 at one side of the reversible rolling mill 7 and at a position within 10 m from the reversible rolling mill 7 between passes of a rolling pass and an inter-pass air-cooling step for air-cooling the steel plate 3 at the other side of the reversible rolling mill 7 after the inter-pass water-cooling step. In the inter-pass water-cooling step, the steel plate 3 is once cooled after the steel plate 3 passes through the reversible rolling mill 7 at a rolling pass (N pass), the steel plate 3 is reciprocated, and the steel plate 3 is further cooled before it enters the reversible rolling mill 7 at a rolling pass (N+1 pass). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a thick steel plate, in which a thick steel plate is hot-rolled to manufacture a thick steel plate having a predetermined material and thickness.

In recent years, in hot rolling of thick steel plates, it has been required to produce thick steel plates with excellent strength and toughness. As an example of such a production method, controlled rolling (CR) is applied to the rolled material. By applying, a thick steel plate made of an excellent material is made.
Controlled rolling refers to rolling a slab heated to 1000 ° C or higher to a predetermined plate thickness, and then to the finished plate thickness in a state where the temperature of the rolled material is in the non-recrystallization temperature range or a temperature range close to that temperature range. Rolling is performed. For example, after heating a slab having a thickness of 200 to 300 mm to about 1100 to 1200 ° C., the slab was rolled to about 1.5 to 2 times the finished plate thickness, and then the temperature became 850 ° C. or less which is an unrecrystallized region. Control rolling is started at the time, and rolling is performed to a finished sheet thickness (for example, 15 mm).
Therefore, in order to perform controlled rolling, it is necessary to set the plate thickness and temperature to predetermined values, and usually after rolling the rolled material to the predetermined plate thickness, the vicinity of the rolling mill (reversible rolling mill) The rolled material was allowed to stand in a cool state until reaching the controlled rolling start temperature on the rolling line.

  However, when the temperature at which controlled rolling is performed (controlled rolling start temperature) is low and the thickness of the sheet to be controlled rolled (controlled rolling start thickness) is thick, it takes a considerable time for the rolled material to reach the controlled rolling start temperature. Therefore, there is a problem that idle time is generated in the rolling mill due to the waiting for cooling, and the rolling efficiency is lowered.

In order to solve such problems, a technique for separately installing a temperature adjustment cooling facility to cool the rolled material to a predetermined controlled rolling start temperature and adjusting the steel plate temperature to the controlled rolling start temperature has been proposed. Yes.
In this technique, a reversible rolling mill is used to roll to a predetermined plate thickness, and the rolled material is cooled to a predetermined controlled rolling start temperature with a temperature-controlled cooling facility (temperature-controlled cooling), and then again to a finished plate thickness by a reversible rolling mill. Controlled rolling is performed.

JP 2005-979 A

As described above, the technique described in Patent Literature 1 rolls a rolled material to a control rolling start plate thickness before controlled rolling, adjusts the temperature of the rolled material having a predetermined plate thickness with a temperature-controlled cooling facility, and then reversible again. Control rolling is performed by a type rolling mill.
And in order to avoid interference with a succeeding material, the temperature control cooling equipment is installed in the position about 20 m away from the reversible rolling mill.
Therefore, the rolled material rolled to the control rolling start plate thickness must be moved to a temperature-controlled cooling facility, temperature-adjusted, and further moved to a reversible rolling mill that performs controlled rolling after temperature adjustment. During the process, rolling could not be performed, and there was a problem that idle time was generated in the reversible rolling mill and efficiency decreased.

  The present invention has been made to solve such a problem, and an object of the present invention is to provide an efficient method for producing a thick steel plate without dead time when the thick steel plate is produced by rolling.

The inventor has a problem that the conventional rolling method separates the rolling process and the temperature adjustment process, such as rolling the rolled material to the control rolling start plate thickness and then adjusting the temperature to the control rolling start temperature. I thought it was.
Therefore, the temperature of the rolled material is adjusted in the process of rolling to the control rolling start plate thickness, and when the rolling is completed to the control rolling start plate thickness, the control rolling start temperature is almost reached. And whether temperature adjustment can proceed simultaneously.

In order to roll the rolled material to a predetermined controlled rolling start plate thickness, a plurality of rolling passes are performed, and it is considered that simultaneous progress is possible by performing a cooling process in the middle of the rolling pass. .
However, in the rolling process before the start of controlled rolling (referred to as “pre-rolling process” in this specification), the controlled rolling start temperature may be low and the controlled rolling start plate thickness may be thick. Need to be able to proceed simultaneously.

As a result of the study, unlike the case of rolling a high-temperature rolled material to a predetermined controlled rolling start plate thickness as in the conventional example, a cooling process is performed in the middle of the rolling pass, and further to a predetermined controlled rolling start plate thickness at an early stage. In order to do this, we have learned that it is important how to perform the cooling process in the middle of the rolling pass.
Then, the present invention has been completed by further studying this point, examining steel plates having various finished plate thicknesses, and finding the optimal cooling process.

(1) A method for producing a thick steel plate according to the present invention includes a pre-rolling step in which a steel plate is hot-rolled by a reversible rolling mill to a controlled rolling start temperature and a controlled rolling start plate thickness, and a temperature after the pre-rolling step. A method of manufacturing a thick steel plate comprising a controlled rolling step of performing controlled rolling while controlling the like,
The pre-rolling step includes an inter-pass water cooling step in which the steel sheet is water-cooled at a position within 10 m from the reversible rolling mill between passes of the rolling pass, and after the inter-pass water cooling step. An inter-pass air cooling step of air-cooling the steel plate on the other side of the reversible rolling mill;
The water-cooling process between passes is performed by cooling the steel plate after the steel plate has passed through the reversible rolling mill in a rolling pass (N pass), and moving the steel plate back to move the reversible type in a rolling pass (N + 1 pass). It is characterized by further cooling before entering the rolling mill.

(2) Moreover, the thing as described in said (1) WHEREIN: The said water cooling process between passes cools the said steel plate with the cooling rate of 15-300 degree-C / sec, It is characterized by the above-mentioned.

(3) Moreover, in the thing as described in said (1) or (2), the said water cooling process between passes cools the said steel plate so that it may become a temperature drop amount of 10-200 degreeC, It is characterized by the above-mentioned. is there.

(4) Moreover, the thing in any one of said (1) thru | or (3) WHEREIN: The said water-cooling process between passes cools the said steel plate with the cooling water of flow rate density 4-20m < ³ > / (m < ² > * min). It is characterized by doing.

  According to the present invention, when a thick steel plate is manufactured by finish rolling including controlled rolling, the waiting time for cooling the rolled material can be eliminated, and the productivity of the thick steel plate can be dramatically improved.

It is explanatory drawing of the rolling equipment of the steel plate used for the manufacturing method of the thick steel plate which concerns on one embodiment of this invention. It is the graph which showed the relationship between the rolling temperature in the manufacturing method of the thick steel plate which concerns on one embodiment of this invention, and the time from the start of rolling. It is explanatory drawing of the inter-pass cooling process in the manufacturing method of the thick steel plate which concerns on one embodiment of this invention. It is the graph which showed the relationship between the rolling temperature in the manufacturing method of the thick steel plate which concerns on one embodiment of this invention, and the time from a rolling start in a comparative example.

FIG. 1 is an explanatory view of rolling equipment used in a method for producing a thick steel plate according to an embodiment of the present invention, and a schematic view schematically showing a moving path of a steel plate corresponding to the rolling equipment. .
The rolling equipment 1 shown in FIG. 1 is arranged in the vicinity (position within 10 m) of the table roller 5 that transports the steel plate 3 reversibly, the reversible rolling mill 7 that rolls the steel plate 3, and the reversible rolling mill 7. The cooling equipment 9 is provided.
Each facility will be described in detail.

<Table roller>
The table roller 5 transports the steel plate 3 in a reversible manner at a predetermined transport speed.

<Reversible rolling mill>
The reversible rolling mill 7 reversibly rolls the steel plate 3 with a predetermined rolling force.

<Cooling equipment>

The cooling facility 9 is disposed on one side in the vicinity of the reversible rolling mill 7, and an upper header unit 11 that injects rod-shaped cooling water onto the upper surface side of the steel plate 3, and bar-shaped cooling water is injected onto the lower surface side of the steel plate 3. A lower header unit 13 is provided.
The cooling facility 9 is installed at a position within 10 m with respect to the reversible rolling mill 7. Therefore, the steel plate 3 can be cooled between passes at a position within 10 m from the reversible rolling mill 7.

A method for producing a thick steel plate by rolling the steel plate 3 with the rolling equipment 1 configured as described above will be described.
The manufacturing method according to the present embodiment includes a pre-rolling process in which a steel plate 3 is hot-rolled by a reversible rolling mill 7 to obtain a controlled rolling start temperature and a controlled rolling start plate thickness, and a temperature and the like after the pre-rolling process. A method of manufacturing a thick steel plate comprising a controlled rolling step of performing controlled rolling while controlling,
The pre-rolling process includes a water-cooling process between water passes that cools the steel sheet 3 at one position of the reversible rolling mill 7 and within 10 m from the reversible rolling machine 7 between passes of the rolling pass, and a reversible after the water-cooling process between the passes. An inter-pass air cooling process for air-cooling the steel plate 3 on the other side of the rolling mill 7;
In the water cooling process between passes, the steel plate passes through the reversible rolling mill in a rolling pass (N pass), and then the steel plate is once cooled, and the steel plate is moved backward to perform the reversible rolling in a rolling pass (N + 1 pass). It is designed to be further cooled before entering the machine.

A manufacturing method is demonstrated still in detail based on FIGS. 1-3.
FIG. 2 is an explanatory diagram of a method for manufacturing a thick steel plate according to the present embodiment, in which the vertical axis indicates the rolling temperature (° C.) and the horizontal axis indicates the time (seconds) from the start of rolling. Black circles in FIG. 2 indicate rolling passes.
<Pre-rolling process>
The pre-rolling step is a step in which a slab heated to 1000 ° C. or higher is hot-rolled by a reversible rolling mill 7 to obtain a controlled rolling start temperature and a controlled rolling start plate thickness.
The controlled rolling start temperature is not higher than the non-recrystallization temperature range or a temperature range close to that temperature range (about 850 ° C. or lower). The controlled rolling start plate thickness varies depending on the finished plate thickness, but is usually about 1.5 to 2 times the finished plate thickness.

  In the present invention, an interpass cooling step is provided in the middle of the pre-rolling step. In the inter-pass cooling process in the present embodiment, in FIG. 3, the steel sheet 3 is moved in the right direction in FIG. If the pass to be rolled is (N + 1) pass, after the steel plate 3 passes through the reversible rolling mill 7 in the N pass, the steel plate 3 is water-cooled before entering the reversible rolling mill 7 for the (N + 1) pass. Passing cooling is done. The range of passing cooling by injecting cooling water is preferably about 50 to 200 cm in the steel plate conveyance direction.

  In addition, after the steel plate 3 has passed the reversible rolling mill 7, as can be seen by referring to FIGS. 3 (a), (c) and (e), the portion to be cooled in the steel plate 3 has passed the reversible rolling mill 7. This means the latter, and does not mean that the entire steel sheet passes through the reversible rolling mill 7. Moreover, before entering the reversible rolling mill 7, as can be seen with reference to FIGS. 3B and 3D, it means that the portion to be cooled in the steel plate 3 enters before the reversible rolling mill 7. It does not mean that a part of the rolling mill 7 is not yet entered.

  In the present embodiment, since the cooling equipment 9 shown in FIG. 1 is arranged on one side of the reversible rolling mill 7, the inter-pass cooling step is performed after the steel plate 3 passes through the reversible rolling mill 7 in the N pass. Performed before entering the reversible rolling mill 7 for the (N + 1) pass, but after the steel plate 3 has passed the reversible rolling mill 7 in the (N + 1) pass, for the next rolling pass (next N pass) However, it is not performed before entering the reversible rolling mill 7, and only air cooling is performed during this period.

In the inter-pass cooling step, in the present embodiment, the cooling rate of the steel plate 3 is 15 ° C./sec to 300 ° C./sec, the temperature drop is 10 to 200 ° C., and the cooling water flow density is 4 to 20 m ³ / (m ^2. -Min).
This is the result of obtaining the optimum cooling rate, temperature drop amount, and flow density by performing inter-pass cooling on steel plates having a plurality of types of finished plate thicknesses. The results of the interpass cooling are shown in Table 1.

As shown in Table 1, the cooling rate of the steel sheet 3 is 15 ° C./sec to 300 ° C./sec, the inter-pass temperature drop is 10 to 200 ° C., and the cooling water flow density is 4 to 20 m ³ / (m ² · min). By doing so, it is possible to continuously perform rolling to the target controlled rolling start temperature and the controlled rolling start plate thickness without the cooling waiting time for the steel plates having all the assumed thicknesses. Therefore, rolling time can be shortened and productivity can be improved. If the cooling rate is less than 15 ° C./sec, the temperature drop between passes is less than 10 ° C., or the flow rate density of cooling water is less than 4 m ³ / (m ² · min), the ability to perform inter-pass cooling of the present invention is insufficient. However, if the cooling rate exceeds 300 ° C./sec, the temperature drop between passes exceeds 200 ° C., or the flow rate density of the cooling water exceeds 20 m ³ / (m ² · min), the cooling has unnecessary excessive capacity. It is not economical as a facility.
The steel plate 3 is cooled after passing through the reversible rolling mill 7 in the N pass, and further cooled before passing through the reversible rolling mill 7 for the (N + 1) pass. Is due to this two-pass cooling.
The cooling rate and the temperature drop amount are controlled by adjusting the cooling water amount, the cooling water flow density, the steel plate conveyance speed, the cooling water temperature, and the like.

In addition, as shown in the prior art document 1, before starting the controlled rolling, after rolling to the controlled rolling start plate thickness, how much rolling time is compared with the case of cooling to the controlled rolling start temperature by the cooling equipment. Since we investigated whether it can be shortened, this will be explained.
As a conventional comparative example, a steel sheet having the same finishing plate thickness and controlled rolling start temperature as shown in Table 1 is rolled to the controlled rolling start plate thickness before the controlled rolling, and then controlled rolling by a shower type cooling facility. Table 2 shows the result of manufacturing the thick steel plate by cooling to the starting temperature.

  As can be seen from a comparison between Table 1 and Table 2, for example, when looking at a finished plate thickness of 20 mm (see column D in Tables 1 and 2), the method of the present invention takes 180 seconds, whereas the comparative example takes 214 seconds. It can be seen that the rolling time of 34 sec can be shortened according to the method of the present invention. Looking at other examples, the rolling time is shortened by about 20 to 50 seconds.

  FIG. 4 is a graph showing the relationship between the rolling temperature and the time from the start of rolling for an example of each case of the method of the present invention and the comparative example, where the black circle indicates the method of the present invention and the white triangle indicates the comparative example. . As shown in FIG. 4, in the example of the present invention, the cooling waiting time of the rolling mill does not occur by performing inter-pass cooling, and the time required for finish rolling can be shortened.

  As mentioned above, in this Embodiment, since it cools between passes, rolling, there is no cooling waiting time of a rolling mill, rolling time can be shortened and the manufacturing efficiency of a thick steel plate can be improved.

  Moreover, in this Embodiment, the cooling equipment 9 is installed only in one side of the reversible rolling mill 7, and after the steel plate 3 passes the reversible rolling mill 7 in the N pass, the reversible type for the (N + 1) pass. Cooling between passes is performed only before entering the rolling mill 7, and after the steel plate 3 passes through the reversible rolling mill 7 in the (N + 1) pass, it is air cooled before entering the reversible rolling mill 7 for the next rolling pass. Therefore, the material of the steel plate 3 can be improved by recuperation during the air cooling period. The recuperation refers to a phenomenon in which the surface temperature rises as a result of the temperature gradient between the cooled surface and the inside of the cooling being relaxed over time.

In the above embodiment, the cooling rate of the steel sheet 3 in the inter-pass water cooling is 15 ° C./sec to 300 ° C./sec, the temperature drop is 10 to 200 ° C., and the cooling water flow density is 4 to 20 m ³ / (m. ⁽² · min), it has been explained that the respective values of the cooling rate, the temperature drop amount, and the flow density are defined. However, paying attention to any one of these three parameters, for example, the steel plate 3 Only the cooling rate of 15 ° C./sec to 300 ° C./sec, or only the temperature drop of the steel plate 3 is specified to 10 to 200 ° C., or only the flow density is 4 to 20 m ³ / (m ² · min).

DESCRIPTION OF SYMBOLS 1 Rolling equipment 3 Steel plate 5 Table roller 7 Reversible rolling mill 9 Cooling equipment 11 Upper header unit 13 Lower header unit

Claims (4)

A pre-rolling process in which a steel sheet is hot-rolled by a reversible rolling mill to have a controlled rolling start temperature and a controlled rolling start plate thickness, and a controlled rolling process in which controlled rolling is performed while controlling the temperature and the like after the pre-rolling process. A method for producing a thick steel plate, comprising:
The pre-rolling step includes an inter-pass water cooling step in which the steel sheet is water-cooled at a position within 10 m from the reversible rolling mill between passes of the rolling pass, and after the inter-pass water cooling step. An inter-pass air cooling step of air-cooling the steel plate on the other side of the reversible rolling mill;
The water-cooling process between passes is performed by cooling the steel plate after the steel plate has passed through the reversible rolling mill in a rolling pass (N pass), and moving the steel plate back to move the reversible type in a rolling pass (N + 1 pass). A method for producing a thick steel plate, characterized by further cooling before entering the rolling mill.   The method for producing a thick steel plate according to claim 1, wherein the inter-pass water cooling step cools the steel plate at a cooling rate of 15 to 300 ° C / sec.   3. The method for producing a thick steel plate according to claim 1, wherein in the inter-pass water cooling step, the steel plate is cooled so as to have a temperature drop of 10 to 200 ° C. 3. 4. The thick steel plate according to claim 1, wherein the inter-pass water cooling step cools the steel plate with cooling water having a flow density of 4 to 20 m ³ / (m ² · min). 5. Production method.

Images