JP3391710B2 - Direct heat treatment of hot rolled wire - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for directly heat-treating a hot-rolled wire rod by adjusting and cooling it.

[0002]

2. Description of the Related Art An example of a wire rod hot rolling factory is shown in FIG. 1 as a schematic plan view. In the process of manufacturing a wire rod by hot rolling, in order to effectively use the heat of the wire rod during rolling, after the wire rod immediately after rolling released from the finishing rolling mill 1 is water-cooled in the water cooling zone 2 as necessary, A method of winding the wire in a non-concentric manner by the winding machine 3 and adjusting and cooling while continuously transporting the wire is widely known as a direct heat treatment method of a wire.

In FIG. 1, reference numeral 4 denotes a conveyor,
Reference numeral 5 denotes a wire rod wound in a non-concentric shape, and 6 denotes a focusing device. In recent years, the wire rod hot rolling plant provided with this direct heat treatment process has the following technical trends. ． Due to the demand for high productivity, the rolling speed is increasing. Recently, an example in which a rolling speed exceeding 100 m / sec is adopted has also been reported. ． Due to the demand for diversified quality of wire rods, in addition to simply releasing or forcibly cooling the wire rods during transportation, by adopting heat retention means or heating means, a wider range of cooling speeds or complicated cooling patterns are realized. There have been many attempts to try.

Generally, the equipment is often arranged in a straight line between the finish rolling mill and the winding machine and between the winding machine and the coil focusing machine. There is a problem that the total length of the direct heat treatment line indicated by the distance between the winders (X) and the distance between the winders and the coil concentrator (Y) becomes very long.

That is, if a very long direct heat treatment line is required, a remarkably long factory site or building is required accordingly. In particular, this problem can be a serious problem that cannot be ignored when modifying an existing wire rod rolling factory for the purpose of achieving the above technical trend. In order to solve this problem, the arc-shaped curved conveyor section is added to the transfer conveyor after winding, and even in a remarkably long direct heat treatment line,
It may be possible to install it by effectively using the factory site. FIG. 2 shows an example of a wire rod hot rolling plant arranged based on such a concept. In this example, in order to increase the distance (Y) between the winder and the coil concentrator, the bending conveyors 8 at two locations are used.
-1,8-2 and three straight conveyors 7-1,7-2,7
-3 is arranged.

Regarding a method of conveying a wire rod wound in a non-concentric shape on an arcuate curved conveyor, see, for example, JP-A-57-57.
Japanese Patent No. 145706 discloses an apparatus characterized by the arrangement of transport rollers. In addition, JP-A-5-7084
Japanese Patent Publication No. 2 discloses a direct heat treatment method for uniformly cooling a wire.

[0007]

When a wire rod wound in a non-concentric shape is conveyed by combining an arcuate curved conveyor and a linear straight conveyor, the following problems occur. That is, since the wire rod to be conveyed is a continuous body, a stress that deforms the wire rod coil is generated in the wire rod when entering the straight conveyer from the straight conveyer. This is schematically shown in FIG.

In FIG. 3, the wire material conveyed on the straight conveyor extends on the basis of virtual lines indicated by Z1 to Z2. In the curved conveyor, this is in the state indicated by Z1 'to Z2', and the stress that applies the torsional deformation to the wire acts. Further, when entering the straight conveyor from the curved conveyor, stress that causes deformation in the opposite direction is generated.

When such a stress acts on the wire rod, the scale (iron oxide) that adheres to the surface of the wire rod has a difference in elastic coefficient from the steel portion (base iron portion) of the wire rod (scale is more elastic than steel). May be cracked. Further, when this phenomenon becomes more prominent, a phenomenon may occur in which the scale peels off from the base metal portion.

The state in which the scale is cracked in this way is called "scale cracking". Usually, the wire rod is subjected to pickling or descaling by a mechanical method in a later step, but if there is "scale cracking", a big problem occurs during pickling. That is, during pickling, the cracks of the scale are preferentially corroded by the acid, so that a crack pattern remains on the surface of the wire after descaling, which significantly impairs the commercial value.

On the other hand, when the scale is once peeled and dropped during the direct heat treatment, a strong thin scale layer may be accompanied by the underlying layer, and such a scale is called "double scale". When a wire with "double scale" is mechanically descaled (called mechanical descaling) in the post process, the strong thin scale layer existing on the underlying layer remains and the descaling occurs. Cause defects.

In any case, it should be recognized that directly applying stress to the wire during the heat treatment has a great risk of deteriorating the scale quality. However, in the prior art disclosed in Japanese Patent Application Laid-Open No. 57-145706, only a device provided with a method for correcting the deviation of the center line of the conveyer of the traveling wire rod was developed, and the above-mentioned device is essentially used. It is not intended to reduce or eliminate the stress itself when passing through the curved conveyor.

On the other hand, in the prior art disclosed in Japanese Unexamined Patent Publication (Kokai) No. 5-70842, no consideration is given to the stress generated by passing through the step. Especially in this conventional technology, although it can be evaluated that it is certainly excellent from the viewpoint of uniform cooling, in addition to the stress associated with the passage of the curved conveyor, the stress associated with the passage of the stepped portion should occur. I have no choice but to say that there is a big problem.

It is an object of the present invention to provide a wire rod manufacturing method effective for solving the above problem, that is, a direct heat treatment method for a hot rolled wire rod.

[0015]

In the present invention, first, in order to solve the above-mentioned problems, attention was paid to the temperature of the steel wire rod when passing through the curved conveyor. As is generally well known, the surface scale of the wire produced by hot rolling is from the base metal side to wustite (FeO) and then magnetite (Fe3O).
4), and hetamite (Fe2O3) in the outermost layer. It is generally said that wustite is thickest as compared to other compositions, and relatively thick wustite has better descaling properties in both pickling and mechanical descaling methods.

In the iron-oxygen phase diagram, about 560 ° C.
There is a transformation point of wustite in the vicinity, and wustite has a stable composition above the transformation point. Also, wustite is not formed by oxidation below that temperature. Therefore, if the surface temperature of the wire when the stress caused by the deformation of the wire coil acts on the wire is set to the transformation point of Wustite or higher, the scale problem can be greatly reduced.

That is, if the temperature is at or above the transformation point of wustite, even if cracks, peeling, or detachment occur on the wustite on the surface of the wire rod as a result of stress on the wire rod coil, new formation of wustite occurs. Defects can be repaired. Also, wustite itself is relatively ductile in the high temperature region above its transformation point, causing cracks, peeling, and
There is also an advantage that dropping itself does not occur easily.

For this reason, if the temperature of the wire rod when entering from the straight conveyor to the curved conveyor is set to the Wustite transformation point or higher (wustite stable region), the stress caused by the deformation of the wire coil acts on the wire rod. However, the scale problem described above can be greatly reduced. Further, the next time the wire is subjected to stress is when the wire enters the straight conveyor from the curved conveyor. Also in this case, if the surface temperature of the wire is set to the Wustite transformation point or higher, even if the stress caused by the deformation of the wire coil acts on the wire, the scale problem can be greatly reduced.

Therefore, first of all, according to the present invention, a hot-rolled wire rod is water-cooled, if necessary, and then wound into a non-concentric circle and continuously cooled while being forcibly cooled / cooled / heat-retained.
Direct heat treatment step of adjusting and cooling by combining any one of heating means or a plurality of means is performed on a transfer conveyor composed of both a curved conveyor having an arc shape and a straight conveyor having a straight shape. The surface temperature of the wire to be conveyed is Wustite (F
It is characterized in that an inflection point from the straight conveyor to the curved conveyor or an inflection point from the curved conveyor to the straight conveyor is passed without falling below the transformation point of eO) (claim 1).

On the other hand, after the transformation point of wustite is lowered, it is preferable that stress is not applied to the wire as much as possible from the viewpoint of preventing scale problems. Therefore, in the portion where the wire temperature is equal to or lower than the transformation point, only the curved conveyer or the straight conveyer is arranged, and the curved conveyer or the straight conveyer or the straight conveyer is arranged.
Stress effects due to passage of inflection points of the curved conveyor should be avoided.

The wire material conveyed in a non-concentric shape is shaped and focused into a coil by a focusing device installed at the end of the transport conveyor. In general, to facilitate this focusing task,
Attempts have been made to provide a step on the transfer conveyor immediately before the focusing device and arbitrarily change the transfer speed of the wire before and after the step. This method may be essential for trimming the shape of the coil. If the conveyor is provided with such a step, it is necessary to further arrange the curved conveyor or the straight conveyor.

Therefore, in the second aspect of the present invention, the hot-rolled wire is water-cooled, if necessary, and then wound into a non-concentric shape, and continuously cooled while being forcibly cooled / cooled / heated / heated. The direct heat treatment step of adjusting and cooling by combining any one of the above means or a plurality of means is carried out by a conveyer conveyor composed of both a curved conveyor having an arc shape and a straight conveyor having a straight shape. In the method, the surface temperature of the wire to be conveyed is
The portion below the transformation point of O) is characterized in that it is conveyed only by a curved conveyor having a constant radius of curvature or by a straight conveyor (claim 2).

Further, since the stress is directly applied to the wire material during the heat treatment, the cause of the scale problem is
By avoiding placing the step of the conveyor in the connecting portion of the straight conveyor and the curved conveyor and preventing the stress from increasing synergistically (avoid the bending-induced stress and the step-induced stress from overlapping), The scale problem can be greatly reduced.

Therefore, the present invention according to claim 3 is the same as the above-mentioned claim 1 or 2, in which the curved conveyor having an arc shape is flat without providing a step with a straight conveyor arranged at the front stage or the rear stage or both of them. It is characterized by being made as a simple conveyor.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 4 schematically shows a winder 3 to a focusing device 6 according to an embodiment of the present invention. The finish rolling mill 1 to the winder 3 shown in FIG. I omit it because it is common. In addition, the hot-rolled wire may be water-cooled if necessary, and then wound into a non-concentric shape and continuously conveyed while being forcedly cooled / cooled / heated / heated. The method of carrying out the direct heat treatment step of adjusting and cooling by combining a plurality of means with a transport conveyor constituted by both a curved conveyor having an arc shape and a straight conveyor having a linear shape is the same as in FIG.

In FIG. 4, the transport conveyors are one curved conveyor 8-1 and two straight conveyors 7-1 and 7.
-2. The distance (Y) between the winder and the coil concentrator is about 100 m, and the radius of curvature at the central portion in the width direction of the bending conveyor 8-1 is 5 m. Further, no step is provided between the curved conveyor 8-1 and the front and rear conveyors 7-1 and 7-2.

In the direct heat treatment equipment using this conveyer, the surface temperature of the wire on the inlet and outlet sides of the curved conveyor and the presence / absence of scale problems were investigated and investigated, and shown in Table 1 below.

[0028]

[Table 1]

As is clear from Table 1 above, attention is paid to the harmful effect on the scale quality by the stress acting when the wire passes through the bending conveyor entrance side (the inflection point from the straight conveyor to the bending conveyor). Therefore, in the present invention, the hot-rolled wire rod is water-cooled if necessary, and then wound in a non-concentric shape, and continuously cooled and forcedly cooled / cooled. The direct heat treatment step of adjusting and cooling by combining any one of the heat retention / heating means or a plurality of means is composed of both an arcuate curved conveyor and a linear straight conveyor. In the method performed by a conveyor, the inflection point from the straight conveyor to the curved conveyor without the surface temperature of the conveyed wire falling below the transformation point of Wustite (FeO),
Alternatively, the inflection point from the curved conveyor to the straight conveyor is passed.

Further, in the present invention, the portion where the surface temperature of the wire to be conveyed falls below the transformation point of Wustite (FeO) is conveyed by only a curved conveyor with a constant radius of curvature or only a straight conveyor. Therefore, even if the inflection point is between curved conveyors having different radii of curvature, it is within the scope of the present invention. (The straight conveyor can also be interpreted as a curved conveyor with infinite curvature deformation.)

[0031]

As described in detail above, according to the present invention,
It is possible to provide a direct heat treatment method for hot-rolled wire with good scale quality, and to manufacture good-quality wire.

[Brief description of drawings]

FIG. 1 is a plan view schematically showing a wire rod hot rolling plant equipped with a direct heat treatment facility.

FIG. 2 is a plan view in which a transport conveyor in which a curved conveyor and a straight conveyor are combined is used in order to effectively use the site.

FIG. 3 is an explanatory diagram of stress acting on a non-concentric circular wire rod on a conveyor.

FIG. 4 is a plan view of an essential part showing an embodiment of the present invention.

[Explanation of symbols]

1 Finishing mill 2 Water cooling zone 3 winder 4 Conveyor 5 Non-concentric wire rods 6 Focusing device 7 Direct conveyor 8-curve conveyor

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-70842 (JP, A) JP-A-7-62449 (JP, A) JP-A-7-41867 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C21D 9/52-9/66 C21D 1/00 B21B 43 / 00,45 / 00

Claims (3)

(57) [Claims] 1. A hot-rolled steel wire rod is water-cooled, if necessary, and then wound into a non-concentric shape and continuously conveyed while being forcedly cooled, cooled, kept heat, or heated. In a method in which a direct heat treatment step of adjusting and cooling by combining one means or a plurality of means is carried out by a method in which a conveying conveyor including both curved curved conveyors and straight linear conveyors is used. Hot rolling characterized by passing the inflection point from the straight conveyor to the curved conveyor or the inflection point from the curved conveyor to the straight conveyor without the surface temperature of the wire material falling below the transformation point of Wustite (FeO). Direct heat treatment method for wire. 2. A hot-rolled steel wire rod is optionally water-cooled, then wound in a non-concentric shape, and continuously conveyed while being forcedly cooled / cooled / heated / heated. In a method in which a direct heat treatment step of adjusting and cooling by combining one means or a plurality of means is carried out by a method in which a conveying conveyor including both curved curved conveyors and straight linear conveyors is used. A direct heat treatment method for a hot-rolled wire rod, characterized in that the portion where the surface temperature of the wire rod falls below the transformation point of Wustite (FeO) is conveyed only by a curved conveyor with a constant radius of curvature or by a straight conveyor. 3. The heat according to claim 1, wherein the curved conveyor having an arc shape is a flat conveyor without providing a step with a straight conveyor arranged at a front stage or a rear stage or both of them. Direct heat treatment method for hot rolled material.