JPH09241804A - Pc steel bar excellent in uniform elongation and high temperature relaxation characteristic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a PC steel bar capable of being produced by the ordinary process without requiring a strain application stage, excellent in uniform elongation and high temp. relaxation characteristic, and having >=1420N/mm<2> tensile strength. SOLUTION: This steel bar has a composition containing, by weight, 0.2-0.7% C and 2.0-3.0% Mn and further containing Si and Al so that 2.0wt.%<=Si+ Al<=5.0wt.% is satisfied. Further, this steel bar has <=15% ferrite fraction and >=1420N/mm<2> tensile strength and also has excellent uniform elongation and high temp. relaxation characteristic.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a PC pile and a PC.
The present invention relates to a high-strength / high-ductility PC steel rod having excellent uniform elongation and high-temperature relaxation characteristics used for poles and the like.

[0002]

2. Description of the Related Art PC steel bars are high-strength members used for prestressed concrete. And such P
C steel rod is JIS G 3137 "Thin diameter deformed PC steel rod"
In, the tensile strength, proof stress, elongation, and relaxation value are standardized. However, uniform elongation and high temperature relaxation are not standardized therein.

[0003] Incidentally, a prestressed concrete structure sometimes undergoes bending failure during an earthquake, and it is desired to increase bending toughness in order to prevent the failure. For that purpose, it is known that a PC steel rod having a large uniform elongation is required. In addition, a horizontal restraint bar of concrete may be used together. When concrete is laterally restrained, since it is used in the state where lateral restraint bars are spot welded to PC steel rods, PC steel rods not only have uniform elongation properties before spot welding but also uniform elongation properties after welding. Is needed.

On the other hand, in order to shorten the curing period, the curing of concrete during the production of prestressed concrete piles or balls is often performed by autoclave curing at 180 to 200 ° C. in an atmosphere of about 10 atm. However, autoclave curing has the drawback of increasing the relaxation of PC steel rods in concrete, and P having a small relaxation at such high temperatures.
C steel rod is required.

Improvement techniques have been established for the individual properties of uniform elongation and high temperature relaxation, but PC steel rods excellent in both uniform elongation and high temperature relaxation properties have not yet been established. A slightly superior method for producing a PC steel bar is disclosed in JP-B-3-79410, JP-A-3-28351, and JP-A-58-12.
It is only disclosed in Japanese Patent No. 0738.

Among these, Japanese Examined Patent Publication No. 3-79410 imparts a minute bending strain of 2% or less at the time of tempering, and Japanese Unexamined Patent Publication No. 28351/1990 discloses processing at 900 to 400 ° C. or plasticity. While processing, the temperature is raised to undergo reverse transformation to form an ultrafine structure.
JP-A-120738 discloses cooling with a wet linear machine during straightening.

[0007]

However, in the techniques disclosed in JP-B-3-79410, JP-A-3-28351, and JP-A-58-120738, the steps of imparting strain are all involved. Are required, and the productivity is poor.

The present invention has been made in view of the above circumstances and has a tensile strength of 1420 N / which is excellent in uniform elongation and high temperature relaxation characteristics that can be manufactured in a normal process without requiring a strain imparting process. PC of mm ² or more
The purpose is to provide steel bars.

[0009]

Means for Solving the Problems As a result of repeated research to solve the above problems, the inventors of the present invention have made Si, Al and Mn excellent in uniform elongation and high temperature relaxation characteristics. It was found that the addition of a large amount of is effective.

The present invention has been made on the basis of such findings. First, C: 0.2 to 0.7 wt%,
Mn: 2.0 to 3.0 wt% is contained, Si and Al are further contained so as to satisfy 2.0 wt% ≤ Si + Al ≤ 5.0 wt%, the ferrite fraction is 15% or less, and 1420 N / Disclosed is a PC steel rod excellent in uniform elongation and high temperature relaxation characteristics, which is characterized by having a tensile strength of mm ² or more.

Secondly, the present invention is C: 0.2 to 0.7 w.
t%, Mn: 2.0 to 3.0 wt%, Si and Al are contained so as to satisfy 2.0 wt% ≤ Si + Al ≤ 5.0 wt%, and Ti: 0.01 to 0. 0
5 wt%, B: 0.0003 to 0.005 wt%, M
o: 0.05 to 0.5 wt%, Ni: 0.2 to 1.0 w
t%, Cr: 0.1 to 1.0 wt%, Cu: 0.2 to
1.0 wt%, at least one of them is contained, the ferrite fraction is 15% or less, and the tensile strength is 1420 N / mm ² or more, which is excellent in uniform elongation and high temperature relaxation characteristics. Provided PC steel rod.

The present invention is thirdly, C: 0.2 to 0.5 w.
t%, Mn: 2.0 to 3.0 wt%, and S
i and Al are 2.0 wt% ≦ Si + Al ≦ 5.0 wt
%, The ferrite fraction is 15% or less, and the tensile strength is 1420 N / mm ² or more.
(EN) Provided is a PC steel rod excellent in uniform elongation and high-temperature relaxation characteristics, which is characterized by spot welding and subsequent tempering energization.

Fourth, the present invention is C: 0.2 to 0.5 w.
t%, Mn: 2.0 to 3.0 wt%, Si and Al are contained so as to satisfy 2.0 wt% ≤ Si + Al ≤ 5.0 wt%, and Ti: 0.01 to 0. 0
5 wt%, B: 0.0003 to 0.0050 wt%, M
o: 0.05 to 0.5 wt%, Ni: 0.2 to 1.0 w
t%, Cr: 0.1 to 1.0 wt%, Cu: 0.2 to
1.0 wt%, at least one of them is contained, the ferrite fraction is 15% or less, the tensile strength is 1420 N / mm ² or more, and spot welding and subsequent tempering energization are performed. Provided is a PC steel rod excellent in uniform elongation and high temperature relaxation characteristics.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described specifically. First, the reasons for limiting the components of the present invention will be described.
C is an element necessary to enhance hardenability and strength, and if it is less than 0.2 wt%, the strength level as a PC steel rod cannot be secured. Further, if it exceeds 0.7 wt%, the toughness deteriorates. Therefore, the amount of C is 0.2w
At least t% and at most 0.7 wt%. On the other hand, when spot welding is used, if it exceeds 0.5 wt%, the spot weldability deteriorates. Therefore, in this case 0.2
It is set to be not less than wt% and not more than 0.5 wt%.

Si and Al are used as deoxidizing agents and are effective not only for relaxation characteristics but also for making a great contribution to the improvement of uniform elongation. However, Si +
If the Al value is less than 2.0 wt%, the effect is small, while if it exceeds 5.0 wt%, the toughness decreases and the spot weldability deteriorates. Therefore, the value of Si + Al is set to 2.0 wt% or more and 5.0 wt% or less.

Like M, Mn is a deoxidizing agent and, like C, is an element necessary to enhance hardenability and strength. In addition, the combination with the addition of a large amount of Si and Al has the effect of significantly improving the ductility, especially the uniform elongation property. However, if the amount is less than 2.0 wt%, the effect is small, while if it exceeds 3.0 wt%, the workability or ductility deteriorates. Therefore, the Mn amount is 2.0 to
3.0 wt%.

Each element of Ti, B, Mo, Ni, Cr and Cu is an element that contributes to the improvement of hardenability, and one or more elements are added if necessary. However, if the amount of these is too small, such an effect cannot be obtained, and if the amount is too large, the effect is saturated. Therefore, Ti: 0.01 to 0.05 wt%,
B: 0.0003 to 0.0050 wt%, Mo: 0.0
5 to 0.5 wt%, Ni: 0.2 to 1.0 wt%, C
r: 0.1 to 1.0 wt%, Cu: 0.2 to 1.0 wt
%.

If the ferrite fraction exceeds 15%, the yield point, which is the basic characteristic of the PC steel rod, is less than 1275 N / mm ^2, and the basic characteristics of the PC steel rod are not satisfied. Therefore, the ferrite fraction is set to 15% or less.

The PC steel rod of the present invention is produced by melting a steel having the above-mentioned composition according to a conventional method, rolling it into a round bar, performing an appropriate working, and further performing an appropriate heat treatment such as quenching and tempering. Can be manufactured by.

PC as the material thus obtained
When the steel rod is used for actual prestressed concrete, it is used not only as a raw material but also by spot welding and then tempering and energizing.

[0021]

【Example】

(Example 1) Steel of the present invention having the composition shown in Table 1 (No. 1)
~ 20), comparative steels (No. 21 to 26) were used as test steels, rolled into a rod with a diameter of 8 mm, drawn into a rod with a different diameter of 7.1 mm, and then quenched and tempered by induction heating. . Note that the heat treatment is not limited to high-frequency heating. Here, the quenching heating temperature was 820 to 1150 ° C., and the tempering was performed at an optimum temperature with a tensile strength of 1420 N / mm ² or more as a target.

[0022]

[Table 1]

After that, a tensile test was performed using these as-heat-treated steel bars. The uniform elongation is 2d (d
Is a diameter), and 10d is measured as a gauge length at a distance of 5d or more from the fractured portion.

The relaxation test is conducted according to JIS at room temperature.
G 3137 method. 180 at high temperature
Performed at ℃, add 70% of standard tensile strength stress,
The sample was cooled in the heating pattern shown in (1) and the amount of change in load after 23 hours was measured and evaluated by the ratio with the initial load.

The ferrite fraction was measured by an image analyzer equipped with an optical microscope function. Table 2 shows the results of the tensile test including the uniform elongation thus obtained, the results of the room temperature and high temperature relaxation, and the values of the ferrite fraction.

[0026]

[Table 2]

As shown in Table 2, No. It was confirmed that all of the invention steels 1 to 20 achieved a uniform elongation of 6.5% or more and a high temperature relaxation of 8% or less, and both properties were significantly superior to those of the conventional steel. .

On the other hand, No. 4 among the comparative steels. 21 to No. In No. 23, since the amount of Si + Al was less than 2.0 wt%, uniform elongation and relaxation deteriorated. In addition, No. In No. 24, since the amount of Si + Al exceeds 5 wt% or more, the ferrite fraction becomes too large and the yield point is lowered, and the uniform elongation is also deteriorated. No. 25
Despite having an appropriate chemical composition, since the quenching temperature was low, the yield point was lowered due to the increase in the ferrite fraction. No. In No. 26, since Mn exceeds 3.0 wt%, uniform elongation of 6.5 wt% or more could not be achieved.

(Example 2) In Table 1 above, C is 0.5 w
Spot welding was performed under the welding conditions shown below using a test steel of t% or less, and then a tempering current was applied to the steel and subjected to a tensile test and a relaxation test. The uniform elongation measurement method and the relaxation test method were the same as in the examples.

<Welding conditions> Welding current 2500A Tempering current 2700A Energizing cycle number 2 Pressurizing force 410N Helical muscle SWRM8-3.2mmφ Table 3 shows the results of the tensile test including uniform elongation, and the results of normal temperature and high temperature relaxation.

[0031]

[Table 3] As shown in Table 3, it was confirmed that all the steels of the present invention ensure a uniform elongation of 5% or more by performing tempering energization even after spot welding.

[0032]

As described above, according to the present invention,
There is provided a PC steel rod which can be manufactured by an ordinary process without adding a process such as strain imparting, has a tensile strength of 1420 N / mm ² or more, and is excellent in uniform elongation and high temperature relaxation characteristics. Therefore, the productivity is greatly improved, and the reliability of the prestressed concrete structure is dramatically improved, which is extremely useful in industry.

[Brief description of drawings]

FIG. 1 is a diagram showing a heating pattern when performing high temperature relaxation.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shigeru Mizoguchi 5983 Tamura, Himuratsuka-shi, Kanagawa Pref. 72) Inventor Kazuki Nitta 5893 Tamura, Hiratsuka-shi, Kanagawa Prefecture

Claims (4)

[Claims] 1. C: 0.2 to 0.7 wt%, Mn: 2.
0 to 3.0 wt% and further contains Si and Al so as to satisfy 2.0 wt% ≦ Si + Al ≦ 5.0 wt%, and has a ferrite fraction of 15% or less.
A PC steel rod excellent in uniform elongation and high-temperature relaxation characteristics, which has a tensile strength of 20 N / mm ² or more. 2. C: 0.2 to 0.7 wt%, Mn: 2.
Contains 0-3.0wt%, Si and Al 2.0w
It is contained so as to satisfy t% ≦ Si + Al ≦ 5.0 wt%, and further, Ti: 0.01 to 0.05 wt%, B:
0.0003 to 0.005 wt%, Mo: 0.05 to
0.5 wt%, Ni: 0.2 to 1.0 wt%, Cr:
0.1-1.0 wt%, Cu: 0.2-1.0 wt%,
Containing at least one of these, and having a ferrite fraction of 15
% Or less and a tensile strength of 1420 N / mm ² or more, a PC steel rod excellent in uniform elongation and high temperature relaxation characteristics. 3. C: 0.2 to 0.5 wt%, Mn: 2.
0 to 3.0 wt% and further contains Si and Al so as to satisfy 2.0 wt% ≦ Si + Al ≦ 5.0 wt%, and has a ferrite fraction of 15% or less.
A PC steel rod having a tensile strength of 20 N / mm ² or more, spot welding, and subsequent tempering energization, which is excellent in uniform elongation and high temperature relaxation characteristics. 4. C: 0.2 to 0.5 wt%, Mn: 2.
Contains 0-3.0wt%, Si and Al 2.0w
It is contained so as to satisfy t% ≦ Si + Al ≦ 5.0 wt%, and further, Ti: 0.01 to 0.05 wt%, B:
0.0003 to 0.0050 wt%, Mo: 0.05 to
0.5 wt%, Ni: 0.2 to 1.0 wt%, Cr:
0.1-1.0 wt%, Cu: 0.2-1.0 wt%,
Containing at least one of these, and having a ferrite fraction of 15
% Or less, has a tensile strength of 1420 N / mm ² or more, and is spot-welded and then subjected to tempering energization, which is a PC steel rod excellent in uniform elongation and high-temperature relaxation characteristics.