JP2009241133A - Method of manufacturing bar steel and wire rod - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a line for rolling/manufacturing a bar steel and wire rod and a method of manufacturing the bar steel and wire rod by which the desired product of the bar steel and wire rod is obtained. <P>SOLUTION: In a method of manufacturing the bar steel and wire rod by which the bar steel and wire rod 2 having the final wire diameter of 5.0-21.0 mm in the final wire diameter is rolled under a rolling condition that the rolling speed is 15-110 m/s, the bar steel and wire rod 2 is manufactured so that the difference ΔT1 between the surface temperature after winding of the bar steel and wire rod 2 and the minimum value of the bar steel and wire rod 2 during cooling is ≤150°C. When controlling the surface temperature of the bar steel and wire rod 2, by installing cooling means 9a, 9b, 9c for water-cooling the bar steel and wire rod 2 between the final rolling mill 11 for performing the final rolling of the bar steel and wire rod 2 and a winding reel 8 for winding the bar steel and wire rod 2 which is finally rolled, the flow rate distribution in the cooling means is adjusted. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a strip steel wire.

  A hot rolling mill that continuously rolls steel materials such as billets and blooms to produce bar wire and bar steel, from the upstream side, heating furnace, roughing mill, finish rolling mill, pinch roll, and winder are arranged in order. It is installed. The steel material is heated in a heating furnace and continuously rolled, and then becomes a steel bar wire or a bar steel, and if it is a bar steel wire, it is wound in a ring shape by a winder. In the vicinity of each rolling mill, cooling means is provided for setting the temperature of the strip wire introduced into the rolling mill to a predetermined value. In particular, the control of the cooling means provided between the final rolling mill and the winder is also important in determining the quality of the bar wire and bar steel.

For example, a granular red scale is often generated on the surface of the steel strip after winding, due to the cooling process of the steel strip. The red scale is formed by growing hematite (Fe ₂ O ₃ ) on the outermost layer of the scale in a whisker shape. The occurrence of such a red scale does not affect the properties of the product, but since it is powdery, various problems have occurred, such as drifting in the atmosphere as dust and deteriorating the working environment.
Then, the technique which tries to suppress generation | occurrence | production of a red scale is considered by the cooling method of the bar wire between the last rolling mill and a winding machine (for example, patent document 1).

In the cooling method of the steel bar wire in Patent Document 1, after the steel bar is strongly cooled in the water cooling zone upstream of the final water cooling zone, the recuperation provided between the upstream water cooling zone and the final water cooling zone is performed. Zone, the tensile stress of the outermost layer portion of the strip steel wire at the entry side of the final water-cooling zone is 0 or more, and 1 / of the tensile thermal stress of the outermost layer portion of the strip wire at the outlet side of the upstream water-cooling zone The steel wire was reheated to 2 or less, and the reheated strip wire was weakly cooled in the final water cooling zone.
Japanese Patent Laid-Open No. 08-1232

In the method for cooling a bar steel wire of Patent Document 1, in order to cool (recover) the bar steel wire, a tensile thermal stress of the outermost layer portion of the bar steel wire is required as a control factor. However, it is very difficult to measure the tensile thermal stress during rolling of the steel strip, and even if the tensile thermal stress is determined in advance using a temperature calculation model, the tensile thermal stress is the temperature in the longitudinal direction of the steel strip. There is a problem that it is easy to change due to the distribution, the steel type of the rolled material, the temperature of the cooling water to be cooled with water, the change in cooling capacity due to the transfer of roll wear onto the surface of the wire.
Therefore, there is a problem that it is difficult to reliably suppress the red scale using the technique of Patent Document 1, and it is difficult to keep the quality of the strip wire rod constant.

  Therefore, in view of the above problems, an object of the present invention is to provide a rolling production line for a strip steel wire and a method for producing the strip wire capable of obtaining a desired strip steel wire product.

In order to achieve the above object, the present invention takes the following technical means.
That is, the present invention provides a method of manufacturing a steel strip wire rod having a final wire diameter of 5.0 mm to 21.0 mm under a rolling condition of a rolling speed of 15 m / sec to 110 m / sec. It exists in the point which manufactures a strip steel wire so that temperature may satisfy | fill Formula (1).

In controlling the surface temperature of the strip wire, cooling means for water-cooling the strip wire between a final rolling machine that performs final rolling of the strip wire and a winder that winds the finally rolled strip wire. It is preferable to adjust the flow rate distribution in the cooling means so as to satisfy the formula (1).
In controlling the surface temperature of the strip wire, it is preferable to adjust the entry temperature of the final rolling mill that performs final rolling of the strip wire so as to satisfy the formula (1). Moreover, you may make it adjust the said rolling speed so that Formula (1) may be satisfy | filled.

  It is preferable to manufacture the bar steel wire so that the temperature of the bar steel wire satisfies the formula (2).

  ADVANTAGE OF THE INVENTION According to this invention, the product of the desired strip steel wire can be obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a rolling production line of a steel bar wire that implements the method of manufacturing a steel bar wire of the present invention. In addition, the manufacturing method of the bar wire of this invention is not limited to the rolling manufacturing line of the bar wire shown in FIG. First, the rolling production line 1 will be described.
The rolling production line 1 is for producing the strip wire 2 having a final wire diameter of 5.0 mm to 21.0 mm in a range where the rolling speed (wire speed) is 15 m / sec to 110 m / sec.
The rolling production line 1 includes a heating furnace 3, a descaler 4, a rough rolling mill 5, a middle row rolling mill 6, a finishing rolling mill 7, and a winder 8 for heating steel materials in order from the upstream side to the downstream side. Arranged in order. Further, a plurality of cooling means 9 for cooling the strip steel wire 2 is provided between the intermediate row rolling mill 6 and the winder 8, and the wound strip is wound from the outlet side to the downstream side of the winder 8. A conveyor for conveying the wire 2 is provided. The rolling production line 1 also includes a control device 14 that controls the heating furnace 3, the descaler 4, the roughing mill 5, the intermediate row rolling mill 6, the finishing rolling mill 7, the winding machine 8, and the cooling means 9.

The finish rolling mill 7 includes two rolling mills, and a block mill 10 (VBM) disposed on the downstream side of the intermediate row rolling mill 6 and a sizing mill 11 (on the downstream side of the block mill 10 ( RSM).
On the entry side of the block mill 10, temperature measuring means 12 for measuring the temperature of the strip wire 2 is provided. A temperature measuring means 13 is also provided on the entry side of the sizing mill 11. A temperature measuring means 16 is also provided on the exit side of the winder 8, and the temperature measuring means 16 can measure the surface temperature of the strip wire 2 after winding, that is, a mounting temperature described later. It is like that.

These temperature measuring means 12, 13, and 16 are preferably composed of radiation thermometers. The temperature measuring means 12 and 13 may be provided on the exit side of the block mill 10, the exit side of the sizing mill 11, and the entrance side of the winder 8.
As shown in FIG. 1, three cooling means 9 a, 9 b, 9 c for cooling the strip 2 are provided between the middle row rolling mill 6, the block mill 10, the sizing mill 11, and the winder 8 from the upstream side. They are deployed in order.
Specifically, a first cooling means 9 a is provided between the intermediate row rolling mill 6 and the block mill 10, and a second cooling means 9 b is provided between the block mill 10 and the sizing mill 11. A third cooling means 9 c is provided between the sizing mill 11 and the winder 8.

Each of the cooling means 9a, 9b, and 9c includes a plurality of cooling zones each having a plurality of cooling nozzles. In particular, the third cooling means 9c includes four cooling zones 15a, 15b, 15c and 15d. Each of the cooling zones 15a to 15d is provided in the transfer direction with a predetermined interval.
In the production line 1 of the strip wire 2, when producing the strip wire 2, first, the steel material that is the source of the strip wire 2 is introduced into the heating furnace 3 arranged on the upstream side of the rolling production line 1. Then, the scale attached to the surface of the steel material is peeled off by the descaler 4.

The descaled steel material is rolled to a predetermined size by a rough rolling mill 5 and a middle row rolling mill 6 to form a strip steel wire 2. The strip steel wire 2 is cooled by a first cooling means 9 a and finish-rolled by a block mill 10. To start. The strip wire 2 rolled by the block mill 10 is cooled by the second cooling means 9b and subjected to final rolling by the sizing mill 11. The strip 2 having undergone final rolling is cooled by the third cooling means 9c, wound in a ring shape by the winder 8, and conveyed downstream by a conveyor.
As described above, the bar wire 2 is manufactured. However, when the bar wire 2 is manufactured, in determining the quality of the bar wire 2, the bar wire 2 downstream from the third cooling means 9c is used. Temperature control (management) is very important.

  Therefore, in the present invention, the surface temperature of the bar wire 2 is controlled so that the surface temperature of the bar wire 2 satisfies the formula (1) on the downstream side of the third cooling means 9c.

Hereinafter, temperature control of the strip wire 2 from the third cooling means 9c toward the downstream side will be described.
FIG. 2 shows a strip steel wire 2 having an initial temperature of 1050 ° C. (inlet temperature of the third cooling means 9c), a wire diameter of φ7.5 mm, and a wire speed (rolling speed) of 95 m / sec. Experiments such as simulation of the surface temperature, center temperature, and average temperature of the bar wire 2 from the entry side of the third cooling means 9c to the after winding (placement temperature described later) when cooled in the cooling zones 15a to 15d It is a result.

Specifically, in FIG. 2, the line N <b> 1 indicates the surface temperature of the bar wire 2, the line N <b> 2 indicates the average temperature of the bar wire 2, and the line N <b> 3 indicates the center temperature of the bar wire 2.
The surface temperature after winding the strip 2 is the surface temperature T1 of the strip 2 at the point P1 from the winder 8 on the line N1 and is the temperature after completion of recuperation (surface temperature). T1 may be referred to as a mounting temperature). The temperature difference of the surface temperature of the bar wire 2 after the completion of the cooling by the third cooling means 9c until the winding of the bar wire 2 is represented by ΔT1.
As shown in line N1 in FIG. 2, in the third cooling means 9c, when the strip steel wire 2 is introduced into the most upstream cooling zone 15a (hereinafter sometimes referred to as the first cooling zone 15a), the surface temperature of the strip wire 2 is shown. Is rapidly lowered by the cooling water of the cooling nozzle of the first cooling zone 15a. Thereafter, the surface temperature of the bar wire 2 rises between the first cooling zone 15a and the second cooling zone 15b following the first cooling zone 15a.

In the recuperation region between the first cooling zone 15a and the second cooling zone 15b, the surface is warmed by the heat inside the strip 2 so that the surface temperature rises. On the other hand, from the first cooling zone 15a to the second cooling zone 15b, the average temperature of the strip wire 2 does not drop abruptly compared to the surface temperature, and the average temperature is between the center temperature and the surface temperature. Transition to.
After the surface temperature of the strip steel wire 2 comes out of the cooling zone 15d at the most downstream side of the third cooling means 9c (hereinafter sometimes referred to as the fourth cooling zone 15d), the surface temperature of the strip steel wire 2 gradually increases due to recuperation. The temperature difference after completion of recuperation becomes the above-described temperature difference ΔT1.

The surface temperature of the bar steel wire 2 increases by the temperature difference ΔT1 due to recuperation after the completion of the cooling by the third cooling means 9c and after the winding of the bar wire 2 but the temperature difference ΔT1. In the ascending process (recuperation process), it is conceivable that thermal stress (for example, compressive stress) acts on the surface layer due to thermal expansion of the surface of the strip wire 2.
On the other hand, on the basis of this simulation, it was visually confirmed that no red scale was generated on the surface of the bar wire 2 when the bar wire 2 was rolled with an actual machine.
As a result, it is considered that red scale is generated due to thermal stress caused by recuperation after completion of cooling. That is, as described in JP-A-8-1232, the degree of slip phenomenon between crystals is determined by the stress change in the recuperation process, and the occurrence of red scale is suppressed by suppressing the slip phenomenon. Therefore, it can be said that the thermal stress that causes the slip phenomenon is caused by the red scale.

Since the thermal stress is related to recuperation, it can be estimated that the thermal stress can be approximated by the temperature difference ΔT1.
That is, it is considered that the red scale can be suppressed by paying attention to the temperature difference ΔT1 from the completion of the cooling by the third cooling means 9c to the completion of the winding, and controlling the temperature. As shown in Formula (1), the temperature difference ΔT1 can be expressed as the surface temperature of the strip steel wire 2 after winding and the minimum temperature of the strip wire 2 during cooling.
FIG. 3 summarizes experimental results, such as simulation, on the relationship between the temperature difference ΔT1 of the surface temperature of the strip 2 and the thermal stress. “◯” in FIG. 3 indicates a case where no red scale occurs, and “●” in FIG. 3 indicates a case where a red scale occurs. The determination of the presence or absence of a red scale was made visually.

In the experiment of FIG. 3, rolling was performed by changing the cooling conditions in the actual machine of the rolling production line 1, and the temperature difference ΔT <b> 1 was obtained from actually measured data by a thermometer. The thermal stress was analyzed from a temperature simulation using a computer or the like.
As shown in FIG. 3, the relationship between the temperature difference ΔT1 and the thermal stress is expressed by a linear expression, and it can be correlated with the thermal stress that causes the red scale from the measurable temperature. I understand. It can also be seen that a red scale occurs in the region where ΔT1 exceeds 150 ° C.
As described above, in the present invention, in order to prevent red scale, the temperature after the completion of cooling of the third cooling means 9c (the temperature on the outlet side of the fourth cooling zone 15d) and the temperature after winding of the steel strip 2 ( Cooling is performed so that the temperature difference ΔT1 with respect to the surface temperature T1 of the strip wire 2 at the point P1 from the winder 8 becomes 150 ° C. or less. In other words, the temperature after completion of cooling [the temperature on the exit side of the fourth cooling zone 15d (the temperature on the exit side of the most downstream cooling zone)] can be said to be the minimum value of the surface temperature of the steel bar during cooling. The strip steel wire 2 is cooled so as to satisfy (1).

In general, in order to eliminate an error between the actual value of the mounting temperature and the target value of the mounting temperature, feedback control such as a flow rate in the cooling unit 9 is performed. In the control of the temperature difference ΔT1, It is also possible to combine such controls.
Moreover, in order to make temperature difference (DELTA) T1 become 150 degrees C or less, you may adjust the flow distribution for each cooling zone 15 of the 3rd cooling means 9c, or it may be upstream of the 3rd cooling means 9c. The inlet side temperature of the sizing mill 11 (final rolling mill) may be adjusted by cooling the first cooling means 9a or the second cooling means 9b. Furthermore, you may adjust the rolling speed in the rolling production line 1 so that temperature difference (DELTA) T1 may be 150 degrees C or less.

  In addition, the flow rate distribution (the respective flow rates of the first cooling zone 15a, the second cooling zone 15b, the third cooling zone 15c, and the fourth cooling zone 15d) in which the red scale does not occur is determined in advance in the third cooling means 9c. A table may be created, the table may be initialized, and rolling may be performed based on the table. The temperature after completion of cooling of the third cooling means 9c (temperature on the outlet side of the fourth cooling zone 15d) is measured by installing a temperature measuring means (radiation thermometer) on the outlet side of the fourth cooling zone 15. Alternatively, various rolling conditions such as the rolling speed (linear speed) in the rolling production line 1, the heat transfer coefficient of the strip wire 2, the cooling pattern in the first cooling means 9a to the third cooling means 9c, the temperature of the cooling water, etc. May be estimated by calculation.

  Table 1 summarizes the results of experiments conducted on actual machines so that the temperature difference ΔT1 of the strip steel wire 2 is 150 ° C. or less.

In Examples 1 to 8 and Comparative Examples 1 to 3, the cooling zones 15a to 15d (the first cooling zone 15a and the second cooling zone) of the third cooling means 9c are used to control the temperature difference ΔT1 of the strip wire 2. The flow rates in the zone 15b, the third cooling zone 15c, and the fourth cooling zone 15d) were adjusted.
As shown in Example 1 to Example 6, if ΔT1 ≦ 150 ° C., no red scale was generated on the surface of the strip wire 2. On the other hand, as shown in Comparative Examples 1 to 3, a red scale was generated on the surface of the strip steel wire 2 unless ΔT1 ≦ 150 ° C. was satisfied.
In particular, as shown in Example 7 and Comparative Example 2, the flow rate distribution between the first cooling zone 15a and the second cooling zone 15b is made the same, and the flow rate distribution between the third cooling zone 15c and the fourth cooling zone 15d is made. When changed, it is possible to avoid the occurrence of red scale without changing the mounting temperature by intentionally reducing the flow rate of the fourth cooling zone 15d. As shown in Example 8 and Comparative Example 3, even when the flow distribution between the third cooling zone 15c and the fourth cooling zone 15d is different from that in Example 7 and Comparative Example 2, the red scale is maintained without changing the mounting temperature. Can be avoided.

In Example 9 and Comparative Example 4, in controlling the temperature difference ΔT1 of the strip wire 2, the flow rate distribution for each cooling zone 15 of the third cooling means 9 c was constant, and the inlet temperature of the third cooling means 9 c was adjusted. . That is, in Example 9, the temperature was adjusted by varying the amount of water in the first cooling unit 9a and the second cooling unit 9b so that the inlet side temperature of the third cooling unit 9c was lower than that in Comparative Example 4.
When Example 9 and Comparative Example 4 are compared, in Example 9, since the inlet side temperature of the third cooling means 9c is adjusted to be lower than that of Comparative Example 4, even if the winding temperature of both is the same value, The amount of water in the third cooling zone 15c is assumed to be small. As a result, in Example 9, the temperature difference ΔT1 of the strip wire 2 could be reduced from 196 ° C. to 81 ° C., and red scale could be prevented.

In Example 10 and Comparative Example 5, in controlling the temperature difference ΔT1 of the strip steel wire 2, the flow rate distribution for each of the cooling zones 15a to 15d of the third cooling means 9c is constant, and the wire speed (rolling speed) of the strip wire 2 is constant. Adjusted. When Example 10 was compared with Comparative Example 5, in Example 10, the linear speed was reduced so that the temperature difference ΔT1 of the strip wire 2 was 150 ° C. or less, thereby preventing red scale.
As described above, in the method for manufacturing the strip wire according to the present invention, the red scale is prevented if the temperature difference ΔT1 from the completion of the cooling in the third cooling means 9c to the winding in the winder 8 is 150 ° C. or less. be able to.

  Moreover, in manufacturing the ultra low carbon steel (ELCH), that is, the steel wire 2 having a [C] of 0.030% by mass or less, the surface temperature of the steel wire 2 may satisfy the formula (2). preferable.

  Table 2 summarizes the temperature difference (ΔT) between the mounting temperature and the surface temperature.

In Table 2, in the third cooling means 9c, the condition A is the four cooling zones 15a to 15d and the cooling water is cooled so that the total flow rate of the cooling water is 240 t / hr. The flow rate was fixed at 240 t / hr and cooling was performed in two cooling zones 15a and 15d. Condition C was similarly performed by fixing the total flow rate at 240 t / hr and cooling in one cooling zone 15d. It is a thing. In conditions E to G, the total flow rate of cooling water is increased to 320 t / hr, and the number of cooling zones is changed in the same manner as in conditions A to C.
The change in the surface temperature of the strip steel wire 2 when the cooling was performed by the third cooling means 9c under each condition was as shown by a line N1 shown in FIGS.

As shown in FIGS. 4 to 7 and Table 2, if the temperature difference ΔT1 between the mounting temperature and the temperature after completion of cooling is very high at 200 ° C. or higher, crystal grain coarsening in the strip steel wire 2 is observed, that is, Most of them were less than FGc 4.0 (Table 2, evaluation “×”). Moreover, if the temperature difference ΔT1 is less than 100 ° C. to less than 200 ° C., crystal grain coarsening in the strip steel wire 2 is suppressed a little, that is, about 10% of what becomes less than FGc 4.0 is included. (Table 2, evaluation “▲”).
Furthermore, when the temperature difference ΔT1 between the mounting temperature and the temperature after completion of cooling is set to 100 ° C. or less, [Equation (2)] is satisfied, no crystal grain coarsening is observed, all of which are FGc 4.0 or more and FGc 4 There was nothing that was less than 0.0 (Table 2, evaluation “◯”).

As described above, when the strip wire 2 after final rolling is cooled by the third cooling means 9c using the rolling production line 1 of the strip wire 2, the red scale is prevented regardless of the steel type by satisfying the formula (1). In particular, when manufacturing the bar wire 2 of ultra-low carbon steel, by satisfying the formula (2) in addition to the formula (1), both the suppression of the red scale and the coarsening of the crystal grains can be achieved. Can be prevented at the same time.
In order to satisfy Equation (2), the flow distribution of each cooling zone of the third cooling means 9c may be adjusted, or the first cooling means upstream of the third cooling means 9c. The inlet side temperature of the sizing mill 11 (final rolling mill) may be adjusted by the cooling of 9a or the second cooling means 9b. Furthermore, you may adjust the rolling speed in the rolling production line 1 so that temperature difference (DELTA) T1 may be 100 degrees C or less. In addition, the flow rate distribution (the respective flow rates of the first cooling zone 15a, the second cooling zone 15b, the third cooling zone 15c, and the fourth cooling zone 15d) at which the coarsening of crystal grains does not occur in the third cooling means 9c is determined. Alternatively, the table may be created, the table may be initialized, and rolling may be performed based on the table.

It is a schematic diagram of a rolling production line. It is the figure which showed the temperature change of the strip steel wire in a 3rd cooling means. It is the figure which showed the relationship between temperature difference (DELTA) T1 of the surface temperature of a strip steel wire, and a thermal stress. It is the figure which showed the temperature change of the bar wire in conditions AC when a wire diameter is 21 mm. It is the figure which showed the temperature change of the bar wire in conditions AC when a linear form is 14 mm. It is the figure which showed the temperature change of the bar wire in conditions EG when a wire diameter is 21 mm. It is the figure which showed the temperature change of the bar wire in conditions EG when a wire type is 14 mm.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rolling production line 2 Thread steel wire 8 Winding machine 9 Cooling means 11 Sizing mill (final rolling mill)

Claims (5)

In the manufacturing method of the strip wire, the strip wire having a final wire diameter of 5.0 mm to 21.0 mm is rolled under the rolling conditions of a rolling speed of 15 m / sec to 110 m / sec.
A method for producing a bar wire, wherein the surface temperature of the bar wire is controlled so that the surface temperature of the bar wire satisfies the formula (1).

  In controlling the surface temperature of the bar steel wire, between the final rolling machine that performs final rolling of the bar steel wire and a winder that winds the final rolled bar steel wire, a cooling means for water-cooling the bar steel wire is provided, The method of manufacturing a bar wire according to claim 1, wherein flow rate distribution in the cooling means is adjusted so as to satisfy the formula (1).   The control of the surface temperature of the strip wire comprises adjusting an entry side temperature of a final rolling mill that performs final rolling of the strip wire so as to satisfy the formula (1). Method of manufacturing the steel bar wire.   In the control of the surface temperature of the said strip steel wire, the said rolling speed is adjusted so that Formula (1) may be satisfy | filled, The manufacturing method of the strip steel wire in any one of Claims 1-3 characterized by the above-mentioned. The method for manufacturing a bar wire according to any one of claims 1 to 4, wherein the bar wire is manufactured so that a temperature of the bar wire satisfies Equation (2).

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