JPH06228656A - Direct heat treatment method for steel wire - Google Patents

Abstract

PURPOSE:To improve the wire drawability and mechanical descaling properties of steel wire by cooling steel wire rod after hot rolling under specified conditions using foam and thereafter executing water cooling. CONSTITUTION:Steel wire rod subjected to hot rolling is cooled from the Ar1 point or above to 400 to 500 deg.C at 5 to 15 deg.C/sec cooling rate by using foam. Successively, it is water-cooled to <=300 deg.C. The foam is a multilayered assembly of single foam bodies present outside of water, the holdability of gas is good and cooling can be executed in a state in which gas and water are uniformly mixed. The control of the cooling rate can be executed by changing the water content in the foam, and uniform cooling can easily be controlled by refining the single foam diameter. In this way, the wire rod excellent in mechanical peeling properties of scales and having excellent mechanical properties can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct heat treatment method for steel wire rods, and more particularly to a direct heat treatment method for steel wire rods which can markedly improve wire drawing workability and mechanical descaling property. In addition, in the present invention, "foam" refers to a state of aggregation of a large number of bubbles separated by thin liquid films.

[0002]

2. Description of the Related Art In directly adjusting and cooling a steel wire rod after hot rolling in a hot rolling line, it is disclosed in Japanese Patent Laid-Open No. 63-62, for example, to use a foam which can be easily controlled and cooled as a cooling medium.
Although proposed in Japanese Patent No. 848, there is a problem that magnetite (blue scale, hereinafter referred to as blue scale) having a thickness of several microns, which has a difficulty in mechanical descaling, is generated on the surface of the obtained steel wire. .

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a direct heat treatment method for a steel wire rod which can remarkably improve the wire drawing workability as well as the mechanical descaling property.

[0004]

Means for Solving the Problems As a result of various investigations by the present inventors, in adjusting and cooling hot-rolled steel wire rods from a temperature of Ar ₁ point or higher by bubbles, a blue scale generation region is generated during the bubble cooling. It was confirmed that the object of the present invention can be achieved by water-cooling a certain temperature range, which is the gist of the present invention.
r A method for direct heat treatment of a steel wire rod, comprising cooling from a temperature of ₁ point or more to 400 to 500 ° C at a cooling rate of 5 to 15 ° C / sec using a foam, and subsequently water cooling to 300 ° C or less. .

In the present invention, in the cooling process after rolling the steel wire rod, cooling is performed by foaming from a temperature of Ar ₁ point or higher to 400 to 500 ° C. even if the diameter of the wire rod or the ring pitch of the loose coil wire rod changes. This is because it is possible to freely control the cooling rate and reduce variations in the cooling rate. Foam is a multi-layered aggregate of single bubbles existing in other than water, has a good gas retaining property, and can be used for cooling in a state where the gas and water are extremely uniformly mixed. Specifically, it is possible to control the cooling rate by changing the amount of water in the foam, and uniform cooling can be easily realized by making the diameter of a single bubble constituting the foam fine.

Here, the lower limit of the cooling rate is limited to 5 ° C./sec, which is the lower limit cooling rate at which a uniform pearlite structure can be obtained, and if the cooling rate is lower than this, the lamellar pearlite structure becomes coarse. And the upper limit is 1
The reason for setting the temperature to 5 ° C./sec is that this is a limit for obtaining a pearlite structure having a lamellar spacing equivalent to that of a wire rod by a normal air patenting (AP) treatment.

In addition, 400 to 50 following the foam cooling
The reason for water cooling from 0 ° C. to 300 ° C. or less is to play a role of preventing blue scale generated by transformation from wustite in this temperature range, and to make the adjustment cooling device compact by rapidly cooling with water, and This is to remove bubbles adhering to the wire. Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic explanatory view of an apparatus for carrying out the present invention. In the figure, 1 is a laying head, 2 is a foam cooling tank, 3 is a water spray nozzle for water cooling, 4 is a focusing tab, 5 is an air carrying zone, and S is a non-concentric ring wound on a conveyor. It is a steel wire rod. The steel wire rod S from the hot finish rolling mill is wound into a non-concentric ring shape by the laying head 1, introduced into the foam cooling tank 2 at a temperature of Ar ₁ or higher, and cooled at a cooling rate of 5 to 15 ° C./sec. 500-400 ° C
After being cooled to 30 ° C, the water spray nozzle 3
It is cooled below 0 ° C. and then focused on the focusing tab 4.

The foam supplied to the foam cooling tank 2 is, for example, a foaming liquid obtained by adding 1.0 wt% of a surfactant to water, and the cooling rate by the foam is controlled by the foaming ratio (foaming ratio) of the foam. It is performed by adjusting the volume (cm ³ ) / liquid volume (cm ³ )) or by adjusting the speed of foam injection from the foam supply nozzle. When the cooling rate is 5 to 15 ° C./sec, the expansion ratio is about 5 times and the foam injection speed is about 0.1 m /
It is about sec. Further, the foam supplied to the foam cooling tank 2 is generated by a foaming device outside the cooling tank. Inside the foaming machine, the foaming liquid is sprayed onto the wire mesh to form a liquid film, and air is passed therethrough to generate foam,
By reducing the mesh opening diameter of the wire mesh, the diameter of a single bubble forming a foam can be reduced to about 0.5 mm to achieve uniform cooling.

The present invention will be described based on examples.

[0011]

【Example】

Steel type: JIS G3506 SWRH 82A equivalent steel (C: 0.82%, Si: 0.27%, Mo: 0.78
%, P: 0.013%, S: 0.006%) hot-rolled into a wire rod having a diameter of 5.5 mm, and then according to the present invention, from the temperature of Ar ₁ point or higher to 5 to 15 ° C./sec. After cooling with foam at a cooling rate of 400-500 ° C., followed by 3
It was water-cooled to 00 ° C or lower.

As a result, as shown in Table 1, the wire rod according to the present invention has a mechanical descaling property (a strain of 6% is applied to the wire rod by a tensile tester) as compared with the wire rod according to the comparative example which is cooled in the air after being foam-cooled. The ratio of residual scale amount to total scale amount) is excellent. In addition, the variation in mechanical properties of the wire is small compared to the wire using the Stelmore method (conventional example) in which air is forcibly blown and cooled,
It also has excellent mechanical descaling.

[0013]

[Table 1]

[0014]

EFFECTS OF THE INVENTION According to the present invention, it is possible to manufacture a wire rod having excellent mechanical peeling property of scales and excellent mechanical properties.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of an apparatus for carrying out the present invention.

[Explanation of reference symbols] 1: Laying head 2: Foam cooling tank 3: Water spray nozzle 4: Focusing tab 5: Atmospheric transportation zone S: Steel wire rod

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Junji Nishino 12 Nakamachi, Muroran City, Hokkaido Inside Nippon Steel Co., Ltd. Muroran Works (72) Inventor Hiroshi Sato 12 Nakamachi, Muroran City, Hokkaido Muroran Co., Ltd. Inside the steelworks

Claims (1)

[Claims] 1. A hot-rolled steel wire rod is cooled to a temperature of at least _one point of Ar at a cooling rate of 5 to 15 ° C./sec and a temperature of 400 to 500.
A method for direct heat treatment of a steel wire rod, which comprises cooling to a temperature of 300 ° C. with foam and subsequently cooling with water to 300 ° C. or lower.