JP2003082438A - Low alloy wire rod for pc steel, and pc steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide high tensile strength PC (prestressing) steel which has an elemental wire diameter of >=5.04 mm, has tensile strength of >=230 gf/mm2, and has excellent relaxation properties, and to provide a low alloy wire rod as the steel stock thereof. SOLUTION: The low alloy wire rod for PC steel has a composition containing, by weight, 0.5 to 0.8% C, 0.8 to 2.5% Si, 0.4 to 1.3% Mn, 0.4 to 2.0% Cr, 0.05 to 0.5% V and/or 0.01 to 0.05% Nb, 0.1 to 2.0% Ni and/or 0.03 to 0.1% Mo, and the balance Fe with inevitable impurities, and has a steel structure consisting of a pearlitic structure or a mixed structure of pearlite and ferrite.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PC steel wire such as a PC steel wire and a PC steel stranded wire used for a concrete structure and a low alloy wire material for the steel material.

[0002]

2. Description of the Related Art A conventional PC steel material, for example, a PC steel wire, is a piano wire material generally specified in JIS G3502, which is used as a steel material.
It is manufactured by a method in which wire drawing is performed and then bluing or hot stretching is performed in a temperature range of 300 to 400 ° C. The tensile strength of the PC steel wire obtained by using the piano wire as a steel material in this way is 19 at a material diameter of 5.04 mm.
The limit was 5 kgf / mm2. On the other hand, in recent years, along with the demand for larger size of concrete structures, cost reduction, and shortening of construction period, in combination with the use of high-strength concrete, in order to improve the degree of freedom in design of the entire structure, the PC steel wire has a higher level of flexibility. In addition to the demand for tensioning, there is a demand for materials with excellent relaxation characteristics that can secure prestress even after long-term use, and the above-mentioned conventional PC steel wire cannot fully meet these requirements. It is becoming.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above circumstances, and has a strand diameter of 5.04 mm.
As described above, it is an object to provide a PC steel material having a high tensile strength of 230 kgf / mm 2 or more and excellent in relaxation characteristics and a low alloy wire material as the steel material.

[0004]

As means for solving the above problems, in claim 1 of the present invention, the weight ratio is
C: 0.5-0.8%, Si: 0.8-2.5%, M
n: 0.4 to 1.3%, Cr: 0.4 to 2.0%, V:
0.05-0.5% and / or Nb: 0.01-0.0
5%, Ni: 0.1 to 2.0% and / or Mo: 0.0
A low-alloy wire rod for PC steel, characterized by containing 3 to 0.1%, the balance being Fe and unavoidable impurities, and the steel structure being a pearlite structure or a mixed structure consisting of pearlite and ferrite Is.

According to the second aspect of the present invention, the weight ratio of C: 0.5 to 0.8%, Si: 0.8 to 2.5%,
Mn: 0.4 to 1.3%, Cr: 0.4 to 2.0%,
V: 0.05 to 0.5% and / or Nb: 0.01 to
0.05%, Ni: 0.1 to 2.0% and / or Mo:
A PC steel material containing 0.03 to 0.1%, the balance being Fe and inevitable impurities, and the steel structure being a pearlite structure or a mixed structure composed of pearlite and ferrite. .

The present invention will be described in detail below. First, the reasons for limiting the components of the low alloy wire for PC steel of the present invention will be described. In addition, all the numerical values shown by% showing the ratio of the components mean% by weight.

C is an effective and economical element for increasing strength. As the C content increases, the strength after patenting and the amount of work hardening during wire drawing increase. From this, in order to obtain a high strength steel wire by wire drawing, C
The higher the content, the more advantageous it is. In the present invention, the content is 0.5%. On the other hand, if the C content is too large, "an undercooled structure such as martensite may be generated during rolling and wire breakage may occur during wire drawing in the subsequent step, so the upper limit is set to 0.8%. , C content is 0.5 to 0.8%.

Si is a component necessary as a deoxidizing agent during steel making, and also has the effect of increasing the strength of the base material by forming a solid solution in ferrite, and such an effect is obtained by adding 0.8% or more. Effectively demonstrated. However, not only too much toughness and ductility deteriorate, but also surface decarburization, flaws, etc. increase, so the upper limit is made 2.5%. Therefore, the Si content is 0.8 to 2.5%.

Mn is also an element effective in deoxidizing steel,
4% or more is contained. Further, since Mn has a great effect of improving the hardenability, it is possible to increase the uniformity in the cross section by increasing the content when the rolled wire diameter is large, and to improve the ductility of the steel wire after drawing. Is effective for. On the other hand, if the amount is too large, a supercooled structure of martensite or bainite is likely to be formed in the center segregated portion during rolling, so the upper limit of the content is 1.3%. Therefore, the Mn content is 0.4 to 1.3.
%.

[0010] Cr is 0.4% in order to reduce the lamellar spacing of pearlite and to improve the strength and wire drawing workability of the wire.
The above is contained. On the other hand, if the content exceeds 2.0%, the time required for transformation becomes long, the heat treatment equipment becomes large and the production efficiency decreases, so the upper limit is made 2.0%. Therefore, the Cr content is 0.4 to 2.0%.

Both V and Nb have the effects of improving the hardenability and refining the crystal grains during heat treatment.
Is 0.05% or more, and Nb is 0.01% or more. These components are effective for strengthening when the rolled wire diameter is large, and also strengthen pearlite by forming carbonitrides and precipitation hardening. On the other hand, if the amount is too large, the pearlite transformation is delayed, martensite and bainite are likely to be formed, and the precipitation hardening action of carbonitride is saturated, so that the upper limit of the V content is 0.5% and the Nb content is 0.5%. The upper limit is 0.05%. Therefore, the V content is 0.05 to
0.5%, Nb content 0.01-0.05%.
Either V or Nb is essential in the present invention, and it is not always necessary to include both.

Ni and Mo enhance the hardenability and contribute to the high strength. It is necessary to contain Ni in an amount of 0.1% or more and Mo in an amount of 0.03% or more. However, if too much, a supercooled structure such as martensite or bainite is likely to occur in the center segregated portion during rolling, so that the upper limit of Ni content is 2.0% and the upper limit of Mo content is 0.1%. Regulate. Regarding Ni and Mo, one of them is essential in the present invention, and it is not always necessary to contain both of them.

Next, the structure of the low alloy wire for PC steel of the present invention will be described. The steel structure of this wire must be a pearlite structure or a mixed structure of pearlite and ferrite. In the present invention, such a structure is an essential condition for ensuring the strength and workability (especially wire drawing workability) of the wire. Further, even if some of the supercooled structures such as martensite and bainite are mixed, the above characteristics will be deteriorated. Therefore, it is important that the above structures are entirely included without including these supercooled structures.

Next, as a concrete example according to the present invention, a description will be given of the production results of a high toughness and high tensile strength PC steel wire having a diameter of 5.04 mm and a tensile strength of 230 kgf / mm2 grade. A slab obtained by continuously casting molten steel adjusted to the chemical composition shown in Table 1 has a heating temperature of 1000 to 1300 ° C., and a finishing temperature (finishing rolling end temperature) of 10 to 15 mm after hot rolling at Ar ₃ or more. A wire rod was manufactured. In Table 1, A is the steel of the present invention and B is the comparative steel. The steel structures of these rolled wire rods are shown in Table 2.

Then, this wire is subjected to lead patenting and wire drawing to obtain a steel wire having a diameter of 5.04 mm,
Then, bluing treatment was performed at 350 ° C. for 1 hour. Table 3 shows the relationship between the wire diameter of the rolled wire and the tensile strength (TS) of the steel wire after the bluing treatment. In addition, among the rolled steels B-2, B-3, and B-4 among those shown as comparative steels, since a martensite structure appeared as shown in Table 2, there is a risk of cuppy fracture in the next step, The wire drawing process was stopped.

Further, as shown in FIG. 1, the diameter is 5.04.
mm steel wire side wire 1, diameter 5.26 mm steel wire core wire 2
Wire processing was performed from 7 wires with a nominal diameter of 15.2 mm.
After that, hot stretch treatment (heating: 350 ° C x 10
Sec, load stress: 0.4 x breaking load), then relaxation test (load stress: actual tensile strength of steel wire x 0.7, temperature:
25 ° C., test time: 10 hours). Table 4 shows A-7 according to the invention steel and B-7 according to the comparative steel.
The mechanical properties of the strand and the results of relaxation tests are shown.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

[Table 3]

[0020]

[Table 4]

From the results of the above examples, the PC steel material (diameter 5.04 mm PC steel wire and steel stranded wire) obtained from the low alloy wire material for PC steel material satisfying the steel composition and steel structure according to the present invention is a concrete structure. It can be seen that it has excellent properties as a material used. First, the PC steel wire (single wire)
As can be seen from Table 3, the tensile strength of 235 kgf / mm2 is low and 2 is high.
It has reached 50 kgf / mm2 or more. On the other hand, the comparative steels that do not partially satisfy these compositional structures have a high content of less than 230 kgf / mm2.
In addition, the value of tensile strength (195k
From the viewpoint of gf / mm2), it can be said that the PC steel material of the present invention has a significantly improved strength.

Furthermore, from the results of the relaxation test of the stranded steel wire, the PC steel material of the present invention has a relaxation value which is twice as high as that of the comparative steel, showing that the relaxation characteristics are greatly improved. Prove.

[0023]

As described above, according to the present invention,
With a wire diameter of 5.04 mm or more, its tensile strength is 230 kg
Provided are PC steel materials with high tensile strength of f / mm2 or more and excellent relaxation characteristics, and low alloy wire rods as the steel materials, which make the concrete structure large, shorten the construction period, increase the degree of freedom in design and extend the service life. It can reliably meet the recent demands of, and makes an excellent technical contribution to this field.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a PC steel material (7 strands of steel) in an example of the present invention.

[Explanation of symbols]

1: Side wire 2: Core wire

Claims (2)

[Claims] 1. A weight ratio of C: 0.5 to 0.8%, S
i: 0.8 to 2.5%, Mn: 0.4 to 1.3%, C
r: 0.4 to 2.0%, V: 0.05 to 0.5% and /
Alternatively, Nb: 0.01 to 0.05%, Ni: 0.1 to 2.
PC containing 0% and / or Mo: 0.03 to 0.1%, the balance being Fe and unavoidable impurities, and the steel structure being a pearlite structure or a mixed structure consisting of pearlite and ferrite. Low alloy wire rod for steel. 2. A weight ratio of C: 0.5 to 0.8%, S
i: 0.8 to 2.5%, Mn: 0.4 to 1.3%, C
r: 0.4 to 2.0%, V: 0.05 to 0.5% and /
Alternatively, Nb: 0.01 to 0.05%, Ni: 0.1 to 2.
PC containing 0% and / or Mo: 0.03 to 0.1%, the balance being Fe and unavoidable impurities, and the steel structure being a pearlite structure or a mixed structure consisting of pearlite and ferrite. Steel material.