JPS5933175B2 - Manufacturing method of high-tensile wire rod - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing high-tensile steel bars or steel wires (hereinafter collectively referred to as wire rods).

Conventionally, for example, SBPR110 of JISG-3109
/135 and SBPDI30/145 grade high-strength PC steel bars are made by descaling hot-rolled materials by pickling or mechanical methods, and then applying lubricity by applying lime or chemical conversion coating, and then wire-drawing them. Perform irregular shape processing as necessary,
In addition, heat treatment for quenching and tempering is performed on a separate line for manufacturing.

Such conventional methods require dedicated equipment for descaling, and have low productivity because the process is separated from rolling, descaling, wire drawing, deforming, and heat treatment. In particular, descaling before wire drawing has traditionally been considered an essential process in order to improve the quality of the wire and prevent damage to the wire drawing die.
The pickling process for this purpose involves the problem of waste liquid treatment, and mechanical descaling using a roll bender or the like also requires equipment, which leads to a large cost increase. The present invention has been made with the object of eliminating the above-mentioned problems in manufacturing high-tensile wire rods and efficiently manufacturing high-quality wire rods at low cost.

In addition, the high-tensile-strength wire rod in the present invention is mainly used as a PC steel rod, and refers to both wire rods that have been subjected to deformation processing and those that have not been subjected to deformation processing. The present invention is a high-tensile deformed wire material characterized by a combination of directly regulating and cooling a hot-rolled wire material to turn it into martensite, and drawing the wire material using a roller die without descaling the wire material. The gist is the manufacturing method.

Martensite formation by direct controlled cooling not only means that the quenching treatment that is normally performed after wire drawing is performed using the heat retained in the wire during hot rolling, but also that the surface scale of the controlled cooled wire is reduced. This does not cause any hindrance during wire drawing using a roller die, which will be described later, and produces an extremely large effect in that descaling before wire drawing is not necessary.

Roller dies themselves are already well-known for drawing wire rods, but even with this die, it is difficult to draw wire rods manufactured using normal processes to obtain high-quality wire rods without descaling. It is.

The present inventor has discovered that the scale that occurs in steel wires that have been martensitized by direct cooling from a temperature of 700°C or less after hot rolling, especially steel wires with a specific chemical composition described below, is extremely thin, and that I learned that there is no problem with wire drawing. Products that are wire-drawn or further shaped into different shapes with this scale still attached have a beautiful surface and there is no risk of reducing the commercial value. Naturally, in order to convert a steel wire into martensite, it is necessary to cool the wire at a rate higher than the critical cooling rate.

In the present invention, the purpose of martensitization is not only to obtain predetermined mechanical properties, but also to ensure that the generated surface scale does not become an obstacle in the subsequent wire drawing process. Generally, scale generated at high temperatures depends on the initial temperature and cooling rate of the material, and the amount of scale increases as the material is cooled more slowly from a higher temperature. In order to perform wire drawing without descaling, it is necessary to generate a thin FeO-based scale that is highly rollable.
Normally, when blast cooling a loop coil developed on a conveyor using the Stelmore method, the cooling start temperature is too high and untransformed austenite remains while passing through the conveyor.
Since it is formed into a coil shape by the focusing device, the cooling rate becomes less than the critical cooling rate, and a paynite structure is generated. Moreover, blast cooling from a high temperature generates a large amount of undesirable scale, making it impossible to draw the wire without descaling. The present inventor has discovered that if the wire rod after hot rolling is rapidly cooled to 700°C or less (preferably in the range of 700 to 500°C) by forced cooling such as water cooling, and then controlled cooling is performed, a normal Stelmore type device can be used. It was confirmed that even with blast cooling, the wire was sufficiently martensited before convergence, and a thin scale that could be drawn as is was confirmed as shown in the later examples.

A preferred composition for obtaining a high-strength martensitic steel wire by controlled cooling from such a low temperature is as follows. C: 0.10-0.40% Si: 0.05-1.50% Mn: 0.70-2.50% Cr: 0.10-1.50% and MO: 0.05-0.50 % B: 0.0002 to 0.0050% of one or two remaining Fe and impurities.

The reasons for selecting the contents of the above components are as follows.

C is a component that gives steel the necessary strength and hardenability.

C.O. If it is less than iO%, it is difficult to ensure the required strength.
On the other hand, if it exceeds 0.40%, the ductility and spot weldability necessary for a PC steel bar will be impaired. Si is effective in improving hardenability and strength. If it is less than 0.05%, this effect cannot be expected, and if it exceeds 1.50%, the ductility will deteriorate significantly.

Mu is contained in an amount of 0.70% or more in order to improve hardenability. However, amounts exceeding 2.50% are unnecessary. Cr improves hardenability similarly to Mn.

A suitable content is 0.10 to 1.50%.
MO and B are added singly or in combination in order to further improve the hardenability due to the combined effect with the above-mentioned elements.
MO is 0.05-0.50%, B is 0.0002-0.
It is appropriate that the content be 0.050%.

A steel wire having the above composition is sufficiently martensited even at a relatively slow cooling rate by blast cooling, and the scale produced is preferable as described above. The steel wire that has been turned into martensitic material by direct cooling is sent directly to the wire drawing process without going through the descaling process.

One of the features of the present invention is that this wire drawing is performed using a roller die. The roller die operates on the same principle as general rolling, and uses a combination of VH rolls to apply pressure to the wire and draw it. Descaling is not necessary until the martensitic steel wire is drawn using a roller die under the above conditions, but the omission of this descaling process results in a significant reduction in equipment, materials, labor, etc. bring about. The steel wire drawn to a predetermined diameter with a roller die is
It is either sent to a tempering process or tempered after being shaped into different shapes. High-strength PC steel bars require heat treatment of quenching and tempering, but in the method of the present invention, the steel wire has already been turned into martensite by direct cooling, so the heat treatment after wire drawing or deforming is not necessary. Just tempering is enough. If only martensite is formed, the tensile strength is P.
C steel bar satisfies the specified value, but the yield point is low. Tempering is performed to improve this yield point. Preferably, the heating is by high frequency induction heating. PC steel bars are often required to have linearity and relaxation resistance (especially temperature relaxation at about 180° C.).

In order to provide these properties, it is preferable to perform warm straightening during the cooling process after tempering. Warm straightening is effective in improving relaxation resistance, and the method of the present invention makes use of the heat retained in the steel wire during tempering.
It is also thermoeconomically advantageous. Through this treatment, straightening and imparting relaxation resistance are simultaneously performed. EXAMPLE The manufacture of a deformed high tensile strength PC steel bar will be explained as an example.

Eight types of steel with the composition shown in Table 1 were hot rolled to yield a 7.5%
xij wire rod, and was rapidly cooled to 650° C. by forced water cooling. This was formed into a ring shape using a laying cone, spread on a conveyor, and while being transported at a speed of 0.4 m/Sec, controlled cooling was performed by blast air having a cooling capacity of about 10° C./Sec. Conveyor length is 40m1 Cooling time is 1
QQsec.

For comparison, for the five steel types B, C, D, G, and H,
Blast cooling was performed from 850°C.

Table 2 shows the mechanical properties and scale thickness of the wire rod after the above treatment, and FIG. 1 shows a micrograph (570x magnification) showing the scale formation state of Steel D treated by the method of the present invention.

These wire rods are cut into scaled roller dies (2
set, tandem), machining speed 90m/RrIi
IL. The wire was cooled and drawn from 7.5 mxj to 7.28 mwj without lubrication.

Table 3 shows the processing status of this line. The wire rod drawn by the method of the present invention is cold-processed into an irregular shape (oval shape), and then tempered (450
°C) was performed. Furthermore, a spinner-type straightening machine was placed at a position approximately 5 m from the output side of the high-frequency coil, and the bending of the wire was 6 mvt/
1. It was corrected so that it was within 5 m. The inlet temperature of the straightening machine was 440°C. Note that the processing from roller die wire drawing to warm straightening was performed continuously on the same line, and the processing speed was 90 m/min.

Table 4 shows the mechanical properties and other properties of the wire after warm straightening. As is clear from the above test results, wire rods made into martensitic material under specified conditions have thinner scales, and can be successfully drawn using a milling die without descaling.

Furthermore, by subjecting the wire to tempering and warm straightening, a wire with good mechanical properties and luxation properties can be obtained. The method of the present invention, which makes it possible to simplify the process by omitting the descaling process and the quenching process and to make the process continuous from wire drawing to straightening, significantly contributes to improving the productivity of high-tensile steel wire rods.

[Brief explanation of the drawing]

Figure 1 is a micrograph (570x magnification) showing the structure and scale formation of a steel wire directly adjusted and cooled by the method of the present invention.
It is.

Claims (1)

[Claims] 1. A high-tensile wire rod characterized in that a wire rod that has been hot-rolled and turned into martensite by controlled cooling from a temperature of 700° C. or lower is drawn with a roller die without going through a descaling process. Production method. 2 Steel wire has C0.10~0.40%, Si0.05~1
．． 50%, Mn0.70~2.50%, Cr0.10~
1.50% and Mo0.05-0.50% and B0.0
002 to 0.0050% of one or two kinds, the balance being Fe and impurities.
A method for producing a high-tensile wire rod as described in Section 1. 3. A method for manufacturing a high-tensile wire rod according to claim 1 or 2, characterized in that a special shape processing is performed after wire drawing. 4. A method for manufacturing a high-tensile steel wire according to claim 1, 2, or 3, characterized in that tempering and warm straightening are performed after wire drawing or shaping.