JP3112129B2 - Controlled cooling method and apparatus for hot rolled steel wire rod - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the controlled cooling of a loose-coil hot-rolled wire using boiling water or hot water as a cooling medium, and more particularly to a method of obtaining a predetermined metal structure over the entire length and cross-section of the wire. The present invention relates to a controllable cooling method and apparatus thereof.

[0002]

2. Description of the Related Art In order to increase the strength of a carbon steel wire rod by a controlled cooling method (EDC process) using boiling water or hot water as a cooling medium, 80 to 95% is required.
Controlled cooling with hot water at ℃ is essential. However, in the conventional controlled cooling method using boiling water or hot water as a cooling medium,
Since the wire is in a loose coil shape, the cooling rate in the coil varies due to the influence of wire overlap, variation in steel material density, and the like. As a result, variation in mechanical properties and abnormal metal structure occurred in the entire length of the wire rod. For example, the standard deviation of variation in tensile strength was actually 20 N / mm ² .

[0003] Further, since the eutectoid transformation position is different for each rolled wire size, complicated operations such as changing the coil conveying speed for each wire diameter have been required to obtain predetermined mechanical properties.

In order to solve these problems, measures have been proposed to mitigate the effects of steel wire overlap by means such as turning conveyors and laying head winding, but this has not been a complete solution. .

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to obtain a predetermined metallographic structure over the entire length of a wire and to reduce variations in mechanical characteristics. It is an object of the present invention to provide a method and an apparatus for controlling and cooling a hot-rolled steel wire rod.

[0006]

To achieve the above object, the cooling method of the present invention focuses on the fact that the magnetic properties change when a loose coil-shaped wire is cooled and undergoes eutectoid transformation. Then, the eutectoid transformation position of the wire on the conveyor in the cooling tank was measured, and in accordance with the measurement results, hot water and air were added to the portion where the steel density of the wire was high and the cooling rate was slow.
It is characterized by injecting a phase-mixed flow to control the difference between the eutectoid transformation end positions in the loose coil. here,
It is preferable that the difference between the eutectoid transformation end positions in the loose coil be within 1.5 m.

[0007] As an apparatus for carrying out the method, a hot-rolled wire in the form of a loose coil is immersed in a cooling medium of a cooling tank, and the hot-rolled wire is conveyed by a conveyor in the tank. In the cooling device, a magnetic detector for measuring the eutectoid transformation position of the wire is arranged on the upper surface or the lower surface of the conveyor, and in accordance with the measurement result, the steel material density of the wire is high, and the cooling rate is increased. A two-phase mixed flow injection device of hot water and air for forcibly cooling a slow part is provided.

[0008]

The cooling process of the wire supplied from the laying head to the conveyor in the cooling tank will be described. As shown in FIG. 5 (A), the wire wound in a ring shape is non-concentric at substantially constant intervals. And transported in warm water as a cooling medium. Here, looking at the overlap of the wires, the center of the ring is the roughest, and it becomes denser toward both ends (the direction orthogonal to the wire advancing direction). Therefore, simply cooling such a wire uniformly cools only the central portion earlier and cools both ends later.
As a result, the eutectoid transformation position is greatly shifted in the wire rod advancing direction as shown in the figure, and the above-described problem occurs.

[0009] On the other hand, when the wire is cooled in the cooling bath, the steel is transformed from austenite to pearlite, whereby the magnetism is also changed from paramagnetic to ferromagnetic. The present invention pays attention to the above points, measures the eutectoid transformation position of the wire rod on the conveyor with a magnetic detector, and based on the measurement result, forcibly cools both ends of the slow cooling ring-shaped coil. This is to minimize the displacement of the eutectoid transformation position in the wire rod traveling direction.

In the range where the forced cooling is performed, if the density of the central part of the ring is set to 1 due to the overlapping state of the wires, the density of the other parts is expressed as a ratio of the steel wire density (FIG. 5).
(See (B)), for example, a portion having the same density of 1.3 or more may be subjected to forced cooling. As will be described in detail later, if the difference between the eutectoid transformation end positions in the ring is within 1.5 m, a product having uniform mechanical properties can be obtained over the entire length of the wire.

[0011]

An embodiment of the present invention will be described below. First,
The apparatus used in the method of the present invention will be described first. 1A and 1B show a device of the present invention, wherein FIG. 1A is a side view and FIG. 1B is a plan view. In the figure, reference numeral 1 denotes a laying head for supplying a wound wire in a loose coil shape, and the wire supplied from the laying head is sent to a cooling tank 2. The cooling tank 2 stores hot water 3 (which may be boiling water) serving as a cooling medium, and includes a conveyor 4 for transporting the wire in a loose coil shape.

The cooling bath detects a change in magnetism from paramagnetic to ferromagnetic due to the transformation of the wire from austenite to pearlite, and outputs a signal as a current or voltage. A body detector 5 is attached. In this example, a number of magnetic detectors 5 are arranged on the lower surface of the conveyor 4. The conveyor 4 may be made of a paramagnetic material, such as austenitic stainless steel, so as not to hinder the detection of the eutectoid transformation position. or,
As its configuration, for example, two chains are used,
It did not overlap with the magnetic detector 5.

A two-phase mixed-flow jet device 6 of hot water and air is provided in the cooling tank, and based on the measurement result of the magnetic detector 5, a portion having a high wire rod density and requiring a long time for cooling can be effectively removed. It was configured to be able to cool. The injection device 6
It blows out a two-phase mixed flow of hot water and air at ~ 99 ° C,
As shown in FIG. 2, the loose coil is mounted on both sides of the conveyor 4 so that both sides of the loose coil can be intensively cooled.
Although the device is shown only on one side of the loose coil-shaped wire a in FIG. 1, an injection device is similarly provided on the other side.

The wire a supplied on the conveyor in the cooling tank is immersed in a cooling medium, and is also cooled by the jet from the two-phase mixed flow jetting device 6 of hot water and air.
Thereafter, it is conveyed to the next step by the conveyor 4.

Using the above apparatus, C: 0.82%, S
i: 0.18%, Mn: 0.67% (all weight%)
10mm square carbon steel material is hot rolled to 13mm in diameter,
After preliminary cooling to 00 ° C, a cooling treatment was performed using hot water at 85 to 95 ° C as a refrigerant. The cooling conditions were such that two-phase mixing of hot water and air was applied to the part having a steel density of 1.3 or more (see FIG. 5B) in order to make the cooling strength at both sides of the ring close to the cooling rate at the highest cooling rate. A stream was injected to perform forced cooling. At this time, the injection amount of the two-phase mixed flow of hot water and air was adjusted, and the processing was performed while variously changing the difference in the eutectoid transformation end position. And about the obtained wire, the average tensile strength and the standard deviation of the variation in the ring were calculated | required. The results are shown in the graph of FIG. As shown in the graph, it was found that when the difference between the eutectoid transformation positions was within 1.5 m, the standard deviation in the tensile strength distribution was small, and a product having good mechanical properties over the entire length of the wire was obtained.

An embodiment in which the injection amount of the two-phase mixed flow of hot water and air is adjusted so that the difference between the eutectoid transformation end positions is within 1.5 m, FIG. 3 is a graph showing the tensile strength of the wire obtained by the comparative example without cooling and the standard deviation of its variation. (A)
(B) is the result of the example. As shown in the graph, the comparative example had an average tensile strength of 1245 N / mm ² and a standard deviation of 20.1 N / mm ² , whereas the example had an average tensile strength of 1280 N / mm ² and a standard deviation of 7.3 N / m.
It was confirmed that a product as good as m ² was obtained.

Further, when the product defect rate of the example and the comparative example was examined, it was found that the comparative example was 0.53%, whereas the example was significantly improved to 0.08%. Was confirmed.

[0018]

As described above, according to the method of the present invention, the eutectoid transformation position of a wire on a conveyor is measured by a magnetic detector, and based on the measurement result, a ring-shaped coil having a slow cooling is determined. By forcibly cooling the both sides, the shift of the eutectoid transformation position in the wire advancing direction can be minimized. Accordingly, uniform mechanical properties can be obtained over the entire length of the wire, and the defect rate of the product can be significantly reduced, which is extremely effective in improving the quality. Further, the apparatus of the present invention is the most suitable apparatus for carrying out the method, and the effects of the method of the present invention can be reliably achieved.

[Brief description of the drawings]

FIG. 1 shows a device of the present invention, wherein (A) is a side view,
(B) is a plan view.

FIG. 2 is a perspective view showing an arrangement of an injection device of the device of the present invention.

FIG. 3 is a graph showing variation in tensile strength of a wire rod;
(A) shows a comparative example, and (B) shows a case treated by the method of the embodiment.

FIG. 4 is a graph showing a difference between eutectoid transformation end positions and a standard deviation in tensile strength distribution of the obtained wire.

5A and 5B are diagrams for explaining the definition of the wire rod density, in which FIG. 5A is a plan view showing the overlapping state of the wire rods, and FIG. 5B is a graph showing the density distribution.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laying head 2 Cooling tank 3 Hot water 4 Conveyor 5 Magnetic detector 6 Injection device a Wire rod

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-219417 (JP, A) JP-A-50-104754 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C21D 9/52 104 B21B 45/02 320 C21D 1/00 121 C21D 1/18

Claims (2)

(57) [Claims] 1. A method of controlling and cooling a hot-rolled wire rod in which a loose-coil hot-rolled wire rod is immersed in a cooling medium of a cooling tank and conveyed by a conveyor in the tank. The eutectoid transformation position in the wire is measured, and in response to this measurement result, a two-phase mixed flow of hot water and air at 70 to 99 ° C. is applied to the portion where the steel density of the wire is high and the cooling rate is low ,
A method for controlling and cooling a hot-rolled wire, wherein the hot-rolled wire is injected from a two-phase mixed flow injection device, and a difference between eutectoid transformation end positions in a loose coil is set to within 1.5 m. 2. A controlled cooling device for a hot-rolled wire, wherein a loose-coil hot-rolled wire is immersed in a cooling medium of a cooling tank, and is conveyed by a conveyor in the tank. Arrange a magnetic detector for measuring the eutectoid transformation position of the wire on the upper surface or lower surface, and in response to this measurement result, hot water and air forcibly cooling the part where the steel material density of the wire is high and the cooling rate is slow Of the two-phase mixed flow injection device,
The conveyor is a chain of a plurality of rows along a transport direction, is made of a paramagnetic material, and the magnetic detector is disposed between each row of the chain conveyor. Controlled cooling device for rolled wire.