JP2008212965A - Method and equipment for hot-rolling steel bar or wire rod - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolling method and a rolling equipment train by which the surface temperature of steel is effectively raised by induction heating to improve the hot-working property of a hard-to-work material and a material having a thin diameter and also the coarsening of the grain and decarburization of a rolling stock are prevented when hot-rolling steel bars or wire rods. <P>SOLUTION: In this hot-rolling method of the steel bar or the wire rod, when hot-rolling the steel bars or the wire rods with hot-rolling equipment of the steel bars or the wire rods in which a slab heating furnace, a descaler, roughing mill train, an intermediate rolling mill train and a finishing mill train are arranged successively and continuously, the induction heating device is arranged respectively between the plurality of the rolling mills continuously from between the first rolling mill and the second rolling mill of the roughing mill train and, by heating the steel passing through respective rolling mills with an induction heating device, rolling biting surface temperature of the steel in all rolling mills of the roughing mill train (but, the first rolling mill is excepted) and the intermediate rolling mill train is raised. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a steel bar by a hot rolling facility for steel bars or wire rods in which a steel slab heating furnace, a descaler (descaling device), a rough rolling mill row, an intermediate rolling mill row, and a finish rolling mill row are sequentially arranged. In hot rolling of wire, it relates to a hot rolling method and hot rolling equipment for steel bars and wires that can obtain good hot workability of particularly difficult-to-work materials. And it is related with the technique which raises the steel material surface temperature in a rolling process.

The bar / wire is generally manufactured by a hot rolling facility in which a steel slab heating furnace, a descaler, a rough rolling mill row, an intermediate rolling mill row, and a finishing rolling mill row are sequentially arranged.
In particular, when hot-rolling difficult-to-work materials such as free-cutting steel and spring steel, and small-diameter bars and wires, increasing the steel temperature during rolling is advantageous for obtaining good hot workability. Means.
Conventionally, in order to increase the steel material temperature during rolling, in Patent Document 1, for example, when a wire rod is manufactured by continuous rolling after rough rolling by a triple rolling mill, the surface of the steel material is formed by an induction heating device in the process of continuous rolling. A heating technique is disclosed.
Further, for example, Patent Document 2 discloses a rolling mill outlet guide in which an induction heating apparatus that can be effectively applied to a rough rolling mill row of a hot rolling line for bar wires is installed.
Japanese Patent Laid-Open No. 02-99204 Japanese Patent Laid-Open No. 2001-300623

When hot-rolling bars and wire rods with a hot rolling facility in which the above steel slab heating furnace, descaler, rough rolling mill row, intermediate rolling mill row, and finishing rolling mill row are sequentially and continuously arranged, The temperature transition of the rolled material extracted from is roughly as follows.
After being extracted from the heating furnace, the temperature is greatly reduced by the descaler, and in the subsequent rough rolling mill row, it further decreases as the rolling progresses. In the rolling equipment, the steel surface temperature is lowest between the latter stage of the rough rolling mill and the first stage of the intermediate rolling mill row.
Therefore, in order to improve the hot workability of difficult-to-process materials and small-diameter materials, it is necessary to increase the steel surface temperature, which is the lowest particularly between the latter stage of the rough rolling mill and the intermediate rolling mill row. In order to prevent coarsening of the rolling material and decarburization, it is necessary to avoid high-temperature heating in a heating furnace.

In the technique disclosed in the above-mentioned Patent Document 1, the basic configuration of the hot rolling facility is different from that targeted in the present invention, and the arrangement position of the induction heating device is a continuous rolling process after rough rolling. It is only described and does not disclose an effective arrangement viewed from the steel material temperature transition of the entire hot rolling line.
Further, the technique disclosed in the above-mentioned Patent Document 2 is provided with a rolling mill outlet guide in which an induction heating device is installed in a rough rolling mill having the same equipment configuration as that of the subject of the present invention. The effective arrangement of the induction heating device viewed from the steel material temperature transition of the entire rolling line is not disclosed.
Furthermore, both patent documents do not mention anything about the heating temperature of the rolling material. In any case, it can be said that it is difficult to obtain good hot workability by preventing the coarsening of crystal grains and decarburization of the rolled material with the disclosed technologies of both patent documents.

  In view of such circumstances, the problem to be solved by the present invention is a steel bar or wire rod in which a steel slab heating furnace, a descaler, a rough rolling mill row, an intermediate rolling mill row, and a finishing rolling mill row are successively arranged. In order to improve the hot workability of difficult-to-process materials and small-diameter materials when hot rolling steel bars and wire rods with hot rolling equipment, the steel materials are taken into account in the steel surface temperature transition of the entire hot rolling line. The present invention provides a method for effectively increasing the surface temperature by induction heating and a rolling facility for carrying out the method. Further, while improving the hot workability, it is possible to increase the grain size and decarburization of the rolled material. It provides a way to prevent.

  In hot rolling of steel bars and wire rods using a hot rolling facility for steel bars or wire rods in which steel slab heating furnace, descaler, rough rolling mill row, intermediate rolling mill row, and finish rolling mill row are sequentially arranged in sequence, It has been found that it is most effective to provide an induction heating device between a plurality of the most upstream rolling mills in the rolling mill row to heat the passing steel material, thereby completing the present invention.

That is, the gist of the present invention is as follows.
(1) Steel bars and wire rods are hot-rolled by means of hot rolling equipment for steel bars or wire rods in which steel slab heating furnaces, descalers, rough rolling mill rows, intermediate rolling mill rows, and finish rolling mill rows are successively arranged. In this case, an induction heating device is provided between each of the plurality of rolling mills continuously from between the first rolling mill and the second rolling mill in the rough rolling mill row, and the induction heating apparatus passes between the rolling mills. The steel bar is heated to increase the rolling biting surface temperature of the steel bar in all rolling mills of the rough rolling mill row (excluding the first rolling mill) and the intermediate rolling mill row. Hot rolling method.
(2) The steel material between the rolling mills by the induction heating device is heated continuously between the first rolling mill and the second rolling mill of the rough rolling mill, and the Nth rolling mill and the (N + 1) rolling mill (N is The steel bar / wire rod hot-rolling method according to the above (1), wherein the steel material passing between the rolling mills up to an integer of 4 or less is heated.
(3) Billet heating by a billet heating furnace by increasing the rolling biting surface temperature of the steel material in the rough rolling mill row and the intermediate rolling mill row by the hot rolling method described in (1) or (2) above. A method of hot rolling steel bars and wires characterized by lowering the temperature as much as possible.
(4) When hot-rolling difficult-to-process or small-diameter steel bars or wires, the steel slab heating temperature in the steel slab heating furnace is 1200 ° C. or less, and the steel materials in all rolling mills of the rough rolling mill and intermediate rolling mill The method of hot rolling steel bars / wires according to (1) or (2) above, wherein the rolling biting surface temperature is 1000 ° C. or higher.
(5) First rolling of a rough rolling mill in a hot rolling facility for steel bars or wire rods in which a steel slab heating furnace, a descaler, a rough rolling mill row, an intermediate rolling mill row, and a finishing rolling mill row are successively arranged. A hot rolling facility for steel bars and wire rods, wherein an induction heating device is provided between each of a plurality of rolling mills continuously from between the mill and the second rolling mill.
(6) The induction heating device is continuously between the N-th rolling mill and the (N + 1) -th rolling mill (N is an integer of 4 or less) from between the first rolling mill and the second rolling mill of the rough rolling mill. The hot-rolling equipment for steel bars and wire rods according to (5) above, which is provided between the rolling mills.

  According to the present invention, the surface temperature of a steel material during hot rolling can be effectively increased, and the hot workability of a difficult-to-work material such as sulfur-containing free-cutting steel or spring steel or a small-diameter material is improved. Can do. Furthermore, while improving the hot workability, it is possible to prevent coarsening of the rolled material and decarburization of the rolled material. As a result, by increasing the rolling biting surface temperature of the steel material, it is possible to reduce the slab heating temperature in the slab heating furnace as much as possible, and the operational effect is extremely large.

As shown schematically in FIG. 1, the hot rolling equipment for steel bars and wires targeted in the present invention includes a steel slab heating furnace, a descaler, a rough rolling mill row, an intermediate rolling mill row, and a finish rolling mill row. The equipment rows are arranged sequentially and sequentially, and after that, cooling equipment is arranged.
2 and 3 show the details of the hot rolling facility. That is, as shown under the horizontal axis in FIGS. 2 and 3, the steel slab heated and extracted in the steel slab heating furnace 1 is removed from the scale by the descaler 2, followed by the rough rolling mill row 3 and the intermediate rolling mill. Continuous rolling is performed in the row 4 and a finish rolling mill row (not shown), and the rolling is rolled to a predetermined diameter. In FIGS. 2 and 3, the rough rolling mill row 3 is illustrated as an example configured with eight rolling mills (# 1 to # 8), but is normally configured with 6 to 10 rolling mills. The 2 and 3, the intermediate rolling mill row 4 shows three rolling mills (# 9 to # 11) and omits the subsequent rolling mills. Consists of a rolling mill.
The rough rolling mill row 3, the intermediate rolling mill row 4, and the finishing rolling mill row (not shown) are each composed of a plurality of horizontal and vertical rolling mills arranged in series. One pass of rolling is applied.

In such hot rolling of steel bars and wires, for example, as shown by the thin wire 6 in FIG. 2, when the steel material is not heated after being extracted from the steel piece heating furnace, the surface temperature of the steel material extracted from the heating furnace is First, it descends greatly due to the high pressure water of the deskeler, and in the subsequent rough rolling mill row, because the rolling speed is slow, heat removal by the rolling roll and heat loss due to heat radiation between the rolling mills rather than processing heat generated by rolling Further, as it is rolled, it will further drop. After the intermediate rolling mill row, as the rolling speed increases, the dissipated heat decreases with respect to the processing heat generation, so the surface temperature rises. Therefore, in the above hot rolling equipment, the intermediate rolling mill from the latter stage of the rough rolling mill row The steel surface temperature becomes the lowest until the first row. In the example shown by the thin line 6 in FIG. 2, the biting surface temperature of the first rolling mill in the intermediate rolling mill row is the lowest.
In order to effectively increase the steel surface temperature in the hot rolling process in such a steel surface temperature transition, the present inventors have conducted induction heating between a plurality of the most upstream rolling mills in the row of rough rolling mills. The present invention has been completed by finding that it is most effective to provide a device to heat the steel material passing through.

That is, the present invention provides an induction heating device between each of a plurality of rolling mills continuously from between the first rolling mill and the second rolling mill in the rough rolling mill row, and each rolling mill is provided with the induction heating apparatus. The steel material passing through is heated to increase the rolling biting surface temperature of the steel material in all rolling mills of the rough rolling mill row and the intermediate rolling mill row.
More specifically, an induction heating device is provided at least between the first rolling mill and the second rolling mill and between the second rolling mill and the third rolling mill. The steel material passing between the two rolling mills is heated, and further, it is provided continuously between subsequent rolling mills between the third rolling mill and the fourth rolling mill.

The reason why the above-mentioned specific matters are used in the present invention is as follows.
The induction heating device is not provided on the rear surface of the descaler where the steel surface temperature is greatly reduced and before the first rolling mill of the roughing mill. After the scale is removed by the descaler, the scale is immediately roughened before the scale is regenerated. This is because it is necessary to bite the first rolling mill of the rolling mill, and it should be avoided to provide an induction heating device and heat.
An induction heating device is provided in each of a plurality of rolling mills continuously from between the first rolling mill and the second rolling mill in the rough rolling mill row, and the induction heating apparatus is passing between the rolling mills. The steel material is heated because the rolling speed is slower than the latter stage of the rough rolling mill where the surface temperature of the rolling mill bites the steel material is the lowest. Heating between the most upstream rolling mills, where heat loss due to heat radiation between the rolling mills is large, provides better heating efficiency, and subsequent rolling makes the temperature distribution in the surface and cross section of the steel material uniform. It is.
It is necessary to increase the heating temperature to a considerably high temperature by using only one heating device between a plurality of rolling mills, and there is an unfavorable situation in terms of quality such that coarse grains are generated on the surface of the steel material. This is because there is a possibility that it will occur, and the induction heating device becomes large-scale, making it difficult to install it in existing rolling equipment.

As described above, it is more effective to heat at a plurality of continuous positions between the most upstream rolling mills in the rough rolling mill row. However, in consideration of equipment costs, induction heating is the first rolling mill of the rough rolling mill. It is preferable to stop between the second rolling mill and the N-th rolling mill and the (N + 1) -th rolling mill (where N is an integer of 4 or less).
In addition, as an induction heating apparatus, what heats 4 surfaces of steel materials simultaneously is applied. In the present invention, the induction heating device was selected from the viewpoint that it can be easily arranged without significantly remodeling the existing rolling mill row and that the rapid heating of the steel slab can be achieved. A commonly used high-frequency induction heating apparatus of 300 Hz to 3000 Hz is suitable, and the target temperature increase temperature range is 10 ° C. to 200 ° C., and it is desirable to arrange as close to the rolling mill entrance as possible. .

In general, the surface temperature of a steel material in a continuous rolling line is the highest in the heating furnace and the lowest in the roughing mill row. Since the minimum temperature of the steel material is determined by the extraction temperature and the rolling speed, and the rolling speed has no degree of freedom due to equipment capacity constraints, the extraction temperature is uniquely determined when the rolling minimum temperature is set.
The minimum required temperature during rolling is a temperature that avoids the two-layer region to ensure rollability, prevents the occurrence of surface flaws due to insufficient deformation resistance and overload of the rolling mill motor, and the heating temperature in the heating furnace is The minimum required rolling temperature can be secured, and the scale loss and the combustion cost are set to the minimum.
Below, the rolling temperature is defined as the steel surface temperature immediately before biting into the rolling mill, and the temperature range is the minimum value of the rolling mill biting temperature and the heating temperature in the heating furnace, and from this minimum value to the maximum value. Is defined as the steel surface temperature range, and the present invention will be described.

Generally, the steel material surface temperature range is 900 ° C to 1200 ° C. However, for example, in addition to sulfur free-cutting steel or sulfur composite free-cutting steel containing S: 0.08 to 0.33% as defined in JIS G 4804, in recent years, the content of S is not limited to BN free-cutting steel. Free-cutting steel with an upper limit increased to 0.6% has been developed, and in difficult-to-work materials such as sulfur-containing free-cutting steel with S as an essential component, the steel material in the pre-rolling machine decreases when the temperature immediately before the rolling mill decreases. In some cases, surface flaws may be generated by being compressed by the next rolling mill without releasing the distortion generated in. Therefore, it is necessary to set the surface temperature immediately before each rolling mill to 1000 ° C. or higher in order to prevent cracking of the steel material and generation of surface flaws. The steel surface maximum temperature needs to be 1200 ° C. or less, preferably 1180 ° C. or less in order to prevent surface flaws due to the generation of coarse grains, and therefore the steel material surface temperature range is 1000 ° C. or more and 1200 ° C. or less, preferably 1180 ° C. Narrower than general materials below.
Furthermore, for example, in the case of a thin wire rod having a diameter of 5.5 mm, the rolling speed restriction in the finish rolling mill row slows down the rough rolling speed, and the heat loss in the rough rolling mill row increases. Keeping it in range becomes increasingly difficult.

In the present invention, a margin is provided for the lower limit value of the allowable temperature range by installing an induction heating device between the rolling mills and raising the rolling minimum temperature. Further, by lowering the heating furnace extraction temperature, a margin is also generated in the upper limit of the allowable temperature range, and the rolling temperature range is narrower than the conventional temperature range.
The induction heating device is preferably installed downstream of the first roughing mill in the row of roughing mills in order to increase the surface temperature of the steel material immediately before the rolling mill and release the distortion generated in the pre-rolling mill. Even if the extraction temperature of the heating furnace is lowered by installing the induction heating device continuously between the uppermost rolling mills of the rough rolling mill row, the intermediate rolling mill from the preceding stage of the rough rolling mill row is reduced. The minimum rolling temperature generated before the first row can be increased. For example, in sulfur-containing free-cutting steel, the heating temperature can be 1200 ° C. or lower, further 1180 ° C. or lower, and the minimum rolling temperature can be 1000 ° C. or higher.

As described above, according to the present invention, the steel surface temperature range during continuous rolling can be narrowed, and difficult-to-work materials, for example, steel types having a narrow allowable range of rolling material surface temperature, such as free-cutting steel, can be obtained by continuous rolling. In manufacturing, the generation of surface flaws can be suppressed. Further, it is possible to obtain a rolled product having a reduced diameter such as a wire product or a bar product by rolling by continuous rolling with excellent productivity.
Furthermore, by arranging the induction heating device continuously from the first roughing mill, the average cross-sectional temperature can be increased from the start of the roughing mill row. Difficult-to-process materials, such as spring steel, have a heavy load on the rolling mill, and if the heating furnace extraction temperature is lowered to suppress decarburization that occurs in the heating furnace, the equipment capacity may be exceeded. Since the equipment capacity of the rolling mill is designed under the conventional temperature conditions, if the induction heating device is installed in the middle of the rough rolling mill row and low temperature extraction is performed, the rolling mill load in the previous stage where the heating device is installed will be higher than before. A growing problem occurs. Therefore, the induction heating device is installed from the first rough rolling mill, and the average section temperature is increased from the start of the rough rolling, thereby minimizing the number of rolling mills where the rolling temperature is lower than before, and difficult processing such as spring steel. It is also possible to lower the temperature at which the material is extracted from the furnace.

  As a test material, a steel piece having a cross-sectional size of 162 mm in width and 162 mm in height of free-cutting steel having the composition shown in Table 1 (unit: mass%) was used.

<Example 1>
FIG. 2 shows the change in surface temperature when the sample material is heated in a heating furnace and then a pass schedule is taken so that the diameter after finish rolling is 9.5 mm. In FIG. 2, the thin wire 6 is a comparative example, and is an example in which the extraction temperature in the steel slab heating furnace is 1130 ° C., and the steel material is not heated with an induction heating device or the like after extraction in the heating furnace. In this comparative example, the rolling minimum temperature of the steel material is lower than 1000 ° C. In FIG. 2, the thick line 7 is an invention example, and the extraction temperature in the slab heating furnace is the same as that in the comparative example, and the second rolling is performed between the first rolling mill and the second rolling mill in the rough rolling mill row. It is the example which heated steel materials with each induction heating apparatus (5a, 5b, 5c) provided between a mill and the 3rd rolling mill, and between the 3rd rolling mill and the 4th rolling mill. In this example of the invention, the minimum rolling temperature of the steel material exceeds 1000 ° C. Table 2 shows the defect rate due to surface defects of the steel material after hot rolling in the comparative example and the invention example. As shown in Table 2, it can be seen that the surface defect rate of the inventive example is reduced as compared with the comparative example.

<Example 2>
FIG. 3 shows the transition of the surface temperature when the test material is heated in a heating furnace and the pass schedule is taken so that the diameter after finish rolling is 5.5 mm. In FIG. 3, a thin wire 6 is a comparative example, in which the extraction temperature in the steel slab heating furnace is 1210 ° C., and the steel material is not heated with an induction heating device or the like after extraction in the heating furnace. In this comparative example, the rolling minimum temperature of the steel material is lower than 1000 ° C. In FIG. 3, a thick line 8 is Invention Example 1, and the extraction temperature in the steel slab heating furnace is the same as that in the comparative example, and is an example in which the steel material is heated by the induction heating apparatus provided in the same manner as in Example 1. In this invention example 1, the rolling minimum temperature of steel materials is over 1000 degreeC. In FIG. 3, the dotted line 9 is Invention Example 2, the extraction temperature in the slab heating furnace is 1160 ° C., the output of the induction heating device is increased, and the rolling temperature transition after induction heating is the same as that of Invention Example 1. This is an example. Table 3 shows the defect rate due to surface flaws of the steel material after hot rolling in Comparative Example and Invention Examples 1 and 2.
As shown in Table 3, the surface defect rate of Invention Example 1 is lower than that of Comparative Example, and in Invention Example 2, it is further reduced.

As shown in Examples 1 and 2, in the sulfur-containing free-cutting steel, when the minimum rolling temperature is below 1000 ° C., the ductility is insufficient, and when it exceeds 1200 ° C., the surface flaws are remarkably increased due to coarse grains. Induction heating is performed on the uppermost stream side of the rolling mill row, the surface flaw is reduced by raising the rolling minimum temperature to 1000 ° C or higher, and further reducing the flaw extraction temperature by lowering the heating furnace extraction temperature. Can be made.
In addition, although the said Example is an Example in sulfur containing free cutting steel, this invention is not limited to the said Example.

The figure which shows the hot rolling flow of the bar and wire of this invention The figure which shows steel material surface temperature transition of Example 1. The figure which shows steel material surface temperature transition of Example 2.

Explanation of symbols

1: Heating furnace 2: Descaler 3: Rough rolling mill row 4: Intermediate rolling mill row 5a, 5b, 5c: Induction heating apparatus # 1 to # 11: Rolling mill No.

Claims (6)

When hot-rolling steel bars and wire rods with a hot rolling facility for steel bars or wire rods in which a steel slab heating furnace, descaler, rough rolling mill row, intermediate rolling mill row, and finishing rolling mill row are sequentially arranged, An induction heating device is provided between each of the plurality of rolling mills continuously from between the first rolling mill and the second rolling mill in the rolling mill row, and the steel material passing between the rolling mills by the induction heating device. Hot rolling of steel bars and wire rods characterized by increasing the rolling biting surface temperature of the steel in all rolling mills of the rough rolling mill row (excluding the first rolling mill) and the intermediate rolling mill row Method. The steel material between the rolling mills by the induction heating apparatus is heated continuously from between the first rolling mill and the second rolling mill of the rough rolling mill (N + 1) rolling mill (N is 4 or less). The steel bar / wire rod hot-rolling method according to claim 1, wherein the steel material passing between the rolling mills up to an integer) is heated. By increasing the rolling biting surface temperature of the steel material in the rough rolling mill row and the intermediate rolling mill row by the hot rolling method according to claim 1 or 2, the billet heating temperature in the billet heating furnace is made as much as possible. A method of hot rolling steel bars and wire rods, characterized by reducing the temperature. When hot-rolling difficult-to-process or small-diameter steel bars or wire rods, the steel slab heating temperature in the slab heating furnace is 1200 ° C. or less, and the rolling biting of the steel materials in all rolling mills of the rough rolling mill and intermediate rolling mills The hot rolling method for steel bars and wire rods according to claim 1 or 2, wherein the surface temperature of the steel is 1000 ° C or higher. In a hot rolling facility for steel bars or wire rods in which a slab heating furnace, a descaler, a rough rolling mill row, an intermediate rolling mill row, and a finishing rolling mill row are sequentially arranged, the first rolling mill and the first rolling mill of the rough rolling mill A hot rolling facility for steel bars and wire rods, characterized in that an induction heating device is provided for each of a plurality of rolling mills continuously from between two rolling mills. The induction heating device includes each of the first rolling mill and the second rolling mill of the rough rolling mill, and continuously between the Nth rolling mill and the (N + 1) rolling mill (N is an integer of 4 or less). The hot rolling facility for steel bars and wire rods according to claim 5, which is provided between rolling mills.

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