JPH01139719A - Manufacture of high-tensile wire rod - Google Patents

Abstract

PURPOSE:To manufacture an inexpensive high-tensile wire rod suitable for providing the desired strength by subjecting a stock to be rolled having a specific composition consisting of C, Si, Mn, and Fe to rolling at a specific temp. and to finish rolling by means of rolls for rolling with a specific roughness and then subjecting the resulting rolled stock to rapid cooling and to winding. CONSTITUTION:A stock to be rolled having a composition consisting of, by weight, 0.10-0.35% C, 0.10-2.00% Si, 1.00-3.0% Mn, and the balance Fe with inevitable impurities is hot-rolled into a wire rod. At this time, rolling is carried out at >=900 deg.C in roughing and intermediate rolling. Subsequently, finish rolling is applied by using rolls for rolling in which surface roughness is regulated to 5-30mum while controlling inlet temp. in finish rolling to 850-950 deg.C. Then, the rolled stock is cooled rapidly down to 500-250 deg.C and wound, which is cooled rapidly at >=5 deg.C/sec cooling rate. By this method, the high-strength wire rod can be stably obtained without adding hardenability-improving elements.

Description

Detailed Description of the Invention <Industrial Application Field> The present invention relates to a method for manufacturing high-tensile wire rods, and in particular, for example, wire drawing, quenching, and tempering in the manufacturing process of high-tensile wire rods such as PC@rods. The present invention relates to a manufacturing method suitable for omitting or simplifying processing.

<Prior art> For example, high-tensile wire rods such as PC steel bars specified in JIS 03109 are usually drawn after removing the secondary scale of the wire rods, and then subjected to a quenching-tempering process to achieve the desired mechanical properties. properties and is used as a member of concrete piles, etc.

These manufacturing processes are becoming more continuous at the customer's end, improving productivity, but recently they have become even more efficient.

From the viewpoint of energy saving, the aim is to omit heat treatment during the manufacturing process or to simplify the tube, and the wire strength of Azurol is approximately 11.
Demand for high-strength wire rods such as 0 kgf/- or more is increasing.

<Problems to be Solved by the Invention> However, in the case of wire produced by such a conventional method, for example, the azurol strength after the Stelmor treatment of the wire for S B P D 1.30/145 is approximately 70 kgf/
At m+i, the microstructure consists of ferrite and pearlite, and since the strength is considerably insufficient as it is, it is clear that heat treatment is required in the post-process.

Various proposals have been made to solve these problems, such as adding hardenability-improving elements such as Cr, No, and V and adjusting cooling conditions, as disclosed in JP-A-55-119134. Some people try to obtain the desired strength by doing so. In this case, a significant increase in cost due to alloying elements added to improve hardenability is unavoidable.

Further, there is a problem in that the adjustment cooling after winding increases the variation in strength.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method for manufacturing a high-strength wire rod that is least expensive and suitable for obtaining a target strength.

Means for Solving the Problems〉 The present invention provides c:o, to ~0.35%, Si
: 0.10 to 2.00%, Mn-: 1. OO~3.
When manufacturing a wire rod by hot rolling a material having a component containing 0% Fe and the balance consisting of Fe and unavoidable impurities, the rolling material is rolled at 900°C or higher in rough rolling 1 and intermediate rolling, and the finishing rolling entry temperature is A rolling roll regulated at 850 to 950°C and given a surface roughness of 5 to 304 is placed in a finishing mill for finish rolling, then quenched to 500 to 250°C, coiled, and then rolled at 5°C/ The above objective is achieved by cooling for more than a second.

For Kusaku The present invention will be explained in detail below.

First, in order to improve hardenability during the heating to finish rolling process,
It requires high temperature heating and high temperature rolling compared to conventional methods. This is because when the material for a PC steel bar is heat treated by varying the heating temperature and cooling rate, as shown in Figure 1, higher heating temperature results in higher hardness when the cooling rate is the same. It is supported. Furthermore, when looking at the change in hardness up to fully quenched composite fibers, it is clear that it is highly dependent on the cooling rate. Conversely, using controlled cooling as a means of increasing strength means that variations in strength are likely to occur. One way to stabilize this is to increase the amount of elements that improve hardenability, but in addition, when it comes to martensite, which is a completely hardened composite fiber, the hardness remains almost constant regardless of the cooling rate. It can be seen that the hardness of the martensitic structure is uniquely determined by the Cl in the steel, which is an important point for the means of the present invention.

Next, when rapidly cooling immediately after high-temperature rolling, stability with respect to the target temperature becomes a problem. In other words, when cooling with water, it is necessary to bring the wire to a predetermined temperature in a very short time due to restrictions on the wire rolling equipment, and the higher the temperature, the more cooling water is required. The present inventors focused on the surface roughness of the rolled material in order to reduce the amount of water and stably obtain a predetermined temperature, and conducted experiments by varying the roll surface roughness of the rebar roll after finish rolling, and the results shown in Figure 2. I got it. The roll surface roughness was varied from the usual approximately 2 μm to approximately 40 pm, and the material to be rolled was a mild steel wire, rolled to a diameter of 8 holes, and cooled with water from a finish rolling temperature of 950° C. to 400° C. As shown in the figure, it is clear that the larger the surface roughness of the Caliba roll, the smaller the amount of water, and the smaller the variation with respect to the target temperature.Furthermore, lubricity is also an issue when drawing high-strength materials. However, from this point of view as well, it is preferable to have appropriate roughness.

Based on these findings, the present invention controls the rolling temperature and surface properties of the rolled wire rod, achieves stable quenching and 11 weave in the water cooling zone after finish rolling, and makes it possible to manufacture wire rods with high strength. be.

The reason for the limitation will be explained below.

(1) Reasons for limiting each component; C: 0.10-0.35% C: The lower limit of C is set at 0.10% to ensure the necessary strength considering the use of PCS + rods, etc., and it is also too high. The upper limit was set at 0.35% because there is a risk of quenching cracking and deterioration of weldability.

Si: 0.10-2.00gt% Si is a necessary element for deoxidizing and strengthening the base material.For this purpose, the lower limit should be 0.10%, and if it is excessive, it will impair weldability. Since this would lead to deterioration and cost increase, the upper limit was set at 2.00%.

Mn: 1.00-3. Owt% Mn is an element that improves hardenability and stabilizes hardenability, and the lower limit is set at 1.0% to ensure strength. Adding more than necessary will increase costs and is a segregated element. Considering its harmfulness, the upper limit was set at 3%.

In addition, for deoxidation and strength adjustment, A/, Ti+ or C
There is no problem in applying r+V or the like to the method of the present invention.

(2) The temperature of the rolled material in rough rolling and intermediate rolling is 900.
C. or higher: In the rough and intermediate rolling rows, it is necessary to increase the hardenability by coarsening the austenite grain size, so the temperature of the rolled material during this period was high-temperature rolling at 900.degree. C. or higher.

(3) Regulating the finish rolling entry temperature to 850 to 950''C; Finish rolling also has the same purpose as rough and intermediate rolling, but the temperature rises considerably due to heat generation during short, high-speed rolling. Therefore, in consideration of temperature controllability in water cooling after finish rolling, the temperature range was set to be narrow, 850 to 950°C.

(4) Rolling rolls with a surface roughness of 5 to 30 μm are placed in the finishing mill for finishing rolling.As mentioned earlier, in the finishing rolling mill, as much as possible should be carried out in consideration of temperature controllability during water cooling. This gives surface roughness to Calivar Roll in order to reduce the amount of cooling water required during water cooling.
5n is required as the lower limit of surface roughness. Although the amount of cooling water decreases as the roll surface roughness increases,
If it is too large, there is a risk that unevenness will remain on the surface of the wire during wire drawing, so the upper limit was set at 30 mm.

It is preferable that the Caliba roll provided with the surface roughness in this range be installed at the latter stage of the finishing rolling train, and there is no need to place any restrictions on the shape, directionality, etc. of the unevenness.

(5) After finish rolling, it is rapidly cooled to 500-250°C and coiled; water cooling is performed in a water-cooling zone provided immediately after exiting the finish rolling machine. At that time, there is no precipitation of ferrite, for example, which may cause a decrease in strength. Since it is necessary to water-cool to a temperature range, the upper limit is set to soo'c, while the lower limit is set to 250° C., although it is sufficient if it is below the Ms point, there is a concern that hardware problems may occur if it becomes too low.

(6) j! : Cool at 5°C/second or more after winding; If the wound wire is left as it is, it may reheat and precipitate high-temperature transformation products such as ferrite. In order to suppress this reheating, it is necessary to cool at least 5° C./sec.

By combining the processes described above, it is possible to manufacture a wire rod having high tensile strength.

<Example> Examples of the present invention will be described below.

Steels A and B having the chemical composition shown in Table 1 were used as test materials.
After vacuum melting 100 kg each of 4 types, C and D, 15
Forged to 0 field angle. When hot rolling these into wire rods of 8 order φ, the penetration temperature from rough rolling to finish rolling, and the surface roughness of the Caliba roll in the finish rolling row.

The subsequent water cooling stop temperature and blast cooling rate after one winding were varied. The rolling and cooling conditions are summarized in Table 2, and the strength (T) of the wire obtained here is shown.

The test results for S,), elongation (FJ), and reduction of area (R, A,) are also shown in Table 2. Note that this test result is based on the length of 3 mm in the longitudinal direction of the obtained wire, excluding the unsteady portion at the front and rear ends.
The length of each ring is 200 from the 3 rings at the divided position.
20 consecutive samples were taken as m, and the average value of a total of 60 samples was shown.

The average 4a and (M) of the intensities (T, S,
Considerably higher strength has been obtained compared to the strength (T, S,) of α8゜9.11, which is fully comparable to, for example, the strength of a PC steel bar after quenching and tempering, and the strength (T , S, )
The variation (σ) is also smaller and better than this comparative example. In addition, in the comparison example 7.10, although the same strength as the inventive example was obtained, the variation was larger than that of the inventive example, the surface roughness of the finish rolling caliber was small, and the cooling This is thought to be due to the large amount of water and the instability of the water cooling stop temperature. Elongation (U,) and aperture (R, A
, ), the inventive example shows the same value as the comparative example. However, the reason why the aperture of the comparative example experiment Nα8 shows a higher value than the inventive example experiments Nα1 and Nα2 is because the strength is considerably low. It is thought that this is because of this.

<Effects of the Invention> As explained above, according to the present invention, a high-strength wire rod can be stably obtained without adding any hardenability-improving elements, so that heat treatment can be omitted or simplified by customers. is possible, which greatly reduces manufacturing costs.
It can be expected to bring about extremely significant effects.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram showing the relationship between the cooling rate and hardness with respect to the heating temperature, and FIG. 2I2I is a characteristic diagram showing the relationship between the surface roughness of the finishing roll and the amount of cooling water. Kawasaki Steel Corporation Figure 1 Cooling rate (°C/sec)

Claims (1)

[Claims] In weight%, C: 0.10-0.35%, Si: 0.1
0 to 2.00%, Mn: 1.00 to 3.0%, and the remainder consists of Fe and unavoidable impurities. Rolling is carried out at 900°C or higher, the finish rolling entry temperature is regulated at 850 to 950°C, and a rolling roll with a surface roughness of 5 to 30 μm is placed in a finishing mill to perform finish rolling. A method for manufacturing a high-tensile wire rod, which comprises rapidly cooling to ~250°C, winding, and then cooling at a rate of 5°C/second or more.