JPS5847455B2 - Manufacturing method of small scale steel wire rod - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for manufacturing steel wire rods with small scale, and more specifically, eliminates pretreatment steps such as pickling or mechanical descaling during secondary processing such as cold wire drawing. , relates to a method for manufacturing a low carbon steel wire rod that can be directly subjected to S secondary processing from a hot rolled wire rod.

Generally, hot-rolled wire rods are water-cooled after passing through a finishing mill, wound, and then air-cooled.

The surface of the hot-rolled wire rod obtained by such a conventional method is
It is covered with three layers of Fe304 and Fe203 and has a thickness of 10 to 25 μm.

If such a wire is subjected to secondary processing as it is, surface scratches will occur and other problems will occur, and smooth processing will not be possible.

For this reason, prior to secondary processing, after pickling and numbering,
Pretreatment for descaling must be performed, such as lime lubrication treatment or mechanical descaling followed by borax treatment.

Such a pretreatment step is unfavorable from the viewpoint of productivity and economy, as it complicates the wire processing steps and directly reflects the processing cost.

There is a strong demand for the development of a method for manufacturing hot-rolled wire rods that can eliminate such steps and efficiently produce sound secondary processed products by directly subjecting the hot-rolled wire rods to five secondary processing steps.

Therefore, the inventors of the present invention have proposed that by preventing the formation of scale, especially hard Fe304, on the surface of hot-rolled wire rods and reducing the thickness of the scale, even if some scale is present, secondary processing can be performed as it is. As a result of intensive research on a method that can effectively prevent scale generation without interfering with the operation of the hot rolling process, we have found that low carbon after passing through the finishing mill in the hot rolling process By controlling the temperature and atmosphere of the steel wire rod, it is possible to suppress the formation of Fe304 with a thin layer mainly composed of FeO, and it can be processed as is/subjected to secondary processing. Discovering that it can be made into a good product and fully approving the present invention 6
It has arrived.

That is, the present invention provides a method for winding a low carbon steel wire rod having a carbon content of 0.15% or less in an inert gas atmosphere at a temperature of about 750° C. or less after passing through a final finishing mill in a hot rolling process.
By immediately quenching, the scale on the surface of the wire is reduced to F.
It is made into a thin layer mainly composed of eO, which makes it possible to perform secondary processing such as cold wire drawing as it is without descaling.

Next, the present invention will be explained in detail.

In the hot rolling process, FeO is formed on the surface of the wire that has passed through the final finishing mill.

When the wire temperature is high, in addition to the development of this FeO layer, further OkoF
e3 o4 and F e 2 0 3 are generated, and a thick scale consisting of these three layers is formed.

According to the method of the present invention, the temperature of the wire after passing through the final finishing mill is kept below about 750°C, and by protecting the wire in a non-oxidizing atmosphere with an inert gas, FeO is generated between the rolling mill and the winding machine. By keeping the amount to a small amount and rapidly cooling such as water cooling immediately after winding, the generation of Fe 3 O 4 can be effectively suppressed, and the generation of Fe 203 can be substantially completely prevented.

In this way, a hot-rolled wire material having a thin scale of about 4 microns or less, consisting of two layers mainly composed of FeO with a trace amount of Fe304, was obtained, and it was possible to directly draw the wire.

The method of the present invention is suitably employed for low carbon steel.

This is because in the case of high carbon steel, a quenched structure occurs partially during rapid cooling from about 750°C, resulting in undesirable results such as wire breakage during wire drawing. , preferably less than about 0.15% C.

The present invention can be practiced using an apparatus such as that shown in FIG. 1, for example.

In the figure, 1 is a wire rod, 2 is a water cooling zone, 3 is a wire guide device, 4 is a winding device, 5 is a cooling chamber, 6 is a water tank, and 9 is a collector for collecting coils. The inside of the cooling chamber 5 is filled with an inert gas such as N2 gas.

The wire rod 1 that has passed through the final finishing mill is cooled down to about 750°C or less, for example, about 700°C, in a water cooling zone 2, passes through a guiding device 3 maintained in an inert atmosphere, and is transferred to a cooling section by a winding device 4. Six pieces are rolled up in a ring shape into a tank 5, and dropped into a water tank 6 where they are rapidly cooled.

The cooled coil 7 is conveyed by a belt conveyor 8 and collected by a collector 9.

Note that the wound coil may be coated with a rust preventive agent or a wire drawing lubricant between the cooling chamber 5 and the collector 9.

For example, by using a phosphate solution having a rust prevention function as the refrigerant in the quenching water tank 6, the wire can be rapidly cooled and rust-prevented at the same time.

Next, the method of the present invention will be specifically explained with reference to Examples.

Example Steel piece of steel type SWRM8 (weight 400 kg, cross-sectional dimension 11
5φ) to a wire diameter of 5.5φ, using the apparatus shown in FIG. , accumulated in the collector 9.

Note that nitrogen gas was continuously supplied into the induction device 2 and the cooling chamber 5 to maintain an inert atmosphere.

The obtained coil was cold drawn using a continuous wire drawing machine.

The processing conditions, scale properties, and cold wire drawing results are shown below.

(A) Processing conditions: Shown in Table 1.

In Table 1, sample materials Arashi 1 and 2 were obtained by the method of the present invention.
The wires were wound in an inert atmosphere by supplying N2 gas at a wire temperature of 750°C or less, and then immersed in a water tank for rapid cooling. It is a material.

Among the comparative materials, A3 and 4 were subjected to N2 gas supply and rapid cooling after winding, but the winding temperature was high, exceeding 750°C, and A5 was tested without N2 gas supply. A6 was subjected to the winding operation, and A6 was not water-cooled after winding.

&7 is due to normal conditions.

(B) Scale set and its thickness: Shown in Table 2.

As is clear from Table 2 above, in the materials of the present invention (Arashi 1 and 2), which were rolled at 750°C or lower in an inert gas atmosphere and immediately quenched, the thickness of FeO was as thin as 2 to 3 μm. , and Fe304 is not viable, or even if it is formed, it is about 1 μm, and the thickness of the entire scale is kept to 3 to 4 μm or less (see Reference Photo 1).

On the other hand, when winding is performed under normal conditions (A.
7), FeO and Fe304 are generated and the scale thickness is 15μ
(It has reached this level (see reference photo 2).

Even if the material is rolled up at 750°C or lower using an inert gas atmosphere, if rapid cooling is not performed after winding up (&6),
A thick F e s 04 of 1.5 to 2μ is generated, and even if rapid cooling is performed, unless an inert gas atmosphere is used (A5)
, the FeO layer is as thick as 4 to 5 μm.

In addition, even if rapid cooling is performed using an inert gas atmosphere, if the winding temperature exceeds 750°C (A
3 and 4), the production of FeO cannot be sufficiently suppressed, and the scale thickness becomes thicker than 4μ.

(Q Wire drawability Using the above sample materials A1 and A7, cold wire drawing was performed using a continuous wire drawing machine.

The wire drawing die schedule is “5.5φ→4.85
4 passes of φ→422 φ→min 3,68 φ→3.2 φ, and the wire drawing speed was 300 m/min at 32φ.

Further, each rod was not descaled, and only the lubricant before the die was drawn with a G trowel.

As a result, sample material Arashi 7 developed surface scale (cracks),
The die was clogged with scale, making wire drawing impossible.

On the other hand, Arashi 1, which is a material of the present invention, could be drawn smoothly without any trouble.

As described above, according to the method of the present invention, the amount of scale generated on the wire surface is extremely small, so secondary processing can be performed without performing treatments such as pickling or mechanical descaling.

Furthermore, if a slight reduction in die life is allowed, lime lubrication and borax treatment subsequent to pickling and mechanical descaling can also be omitted.

[Brief explanation of drawings]

FIG. 1 is a side schematic view schematically showing an example of an apparatus used for carrying out the method of the present invention. 1: Wire rod, 2: Water cooling zone, 3: Wire rod guiding device, 4: Winding device, 5: Cooling room, 6: Water tank, 7: Coil, 8: Belt conveyor, 9: Collector.

Claims (1)

[Claims] Method 6 for producing a low carbon steel wire rod with an IC of 0.15% or less In this method, the wire rod is passed through a hot final rolling mill and then rolled at 75%.
A method for manufacturing a steel wire rod with a small scale, characterized in that direct wire drawing is possible by winding the rod in an inert atmosphere at 0° C. or lower and immediately quenching it.