JPH09241745A - Production of pc steel rod excellent in uniform elongation and high temperature relaxation characteristic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a producing method capable of producing a PC steel rod excellent in uniform elongation of >=1420N/mm<2> tensile strength and high temp. relaxation characteristics without applying a strain applying stage and stages such as reheating treatment. SOLUTION: A steel contg., by weight, 0.05 to 0.35% C and 0.2 to 3.0% Mn and furthermore contg. Si and Al so as to satisfy 2.0<=Si+AL<=5.0% is subjected to hot rolling and is thereafter subjected to direct quenching at a cooling rate of 5 to 50 deg.C/s to form its structure into the one consisting essentially of martensite, by which the PC steel rod excellent in uniform elongation of >=1420N/mm<2> tensile strength and high temp. relaxation characteristics can be produced.

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.

The mechanical properties after spot welding are described in JP-A-48-89816 and JP-B-55-8.
In Japanese Patent No. 577, there is a description regarding the tensile strength and total elongation after spot welding.

On the other hand, in order to improve uniform elongation or high temperature relaxation, a technique of utilizing direct quenching after hot rolling is disclosed in Japanese Examined Patent Publication No. 56-21811.
No. 103313 and Japanese Patent Publication No. 57-40895.

Among these, Japanese Patent Publication No. 56-21811 is for directly quenching steel in which Cr is added in place of Mn, and Japanese Patent Laid-Open No. 52-103313 is characterized by high temperature tempering after direct quenching. It is a thing, and Japanese Patent Sho 57
No. -40895 discloses that steel having a reduced Si content is directly quenched and then subjected to straightening by repeated bending.

[0010]

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.

Further, in the techniques disclosed in JP-A-48-89816, JP-B-55-8577 and the like, the uniformity after spot welding which actually governs the bending toughness of a prestressed concrete structure is disclosed. In addition to not paying attention to the elongation property, there is a drawback that the elongation amount is not sufficient.

Furthermore, Japanese Patent Publication No. 56-21811 and Japanese Unexamined Patent Publication No. 52-10 utilize direct quenching after hot rolling.
Even with the techniques disclosed in Japanese Patent No. 3313 and Japanese Patent Publication No. 57-40895, sufficient uniform elongation cannot be obtained.

The present invention has been made in view of the above circumstances, and has a uniform elongation and a high temperature relaxation property of a tensile strength of 1420 N / mm ² or more without adding a process such as a strain imparting process or a reheating heat treatment. It is an object of the present invention to provide a manufacturing method capable of manufacturing a PC steel rod excellent in heat resistance.

[0014]

Means for Solving the Problems As a result of repeated research to solve the above-mentioned problems, the inventors of the present invention have found that the uniform elongation of the material before spot welding, the uniform elongation after spot welding, and the high temperature relaxation property are determined. In order to make both of them excellent, it has been found that it is effective to add a large amount of Si and Al and to perform direct quenching after hot rolling.

The present invention has been made on the basis of such findings. Firstly, C: 0.05 to 0.35 wt.
%, Mn: 0.2-3.0 wt%, and Si
And Al of 2.0 wt% ≦ Si + Al ≦ 5.0 wt%
After hot rolling the steel containing so as to satisfy
A PC steel rod excellent in uniform elongation and high temperature relaxation characteristics, characterized by having a structure mainly composed of martensite by direct quenching at a cooling rate of 50 ° C./s and having a tensile strength of 1420 N / mm ² or more. A manufacturing method is provided.

Secondly, the present invention is C: 0.05 to 0.3.
5 wt%, Mn: 0.2-3.0 wt%, Si
And Al of 2.0 wt% ≦ Si + Al ≦ 5.0 wt%
To satisfy Nb: 0.01-
0.1 wt%, Ti: 0.01 to 0.05 wt%, B:
0.0003 to 0.005 wt%, Ni: 0.2 to 1.
0 wt%, Cr: 0.1 to 1.0 wt%, Mo: 0.0
Steel containing at least one of 5 to 0.5 wt% and Cu: 0.2 to 1.0 wt% is hot rolled after hot rolling.
A PC steel rod excellent in uniform elongation and high temperature relaxation characteristics, characterized by having a structure mainly composed of martensite by direct quenching at a cooling rate of 50 ° C./s and having a tensile strength of 1420 N / mm ² or more. A manufacturing method is provided.

The present invention is thirdly, C: 0.05 to 0.3.
5 wt%, Mn: 0.2 to 3.0 wt%, and further Si and Al are 2.0 wt% ≦ Si + Al ≦ 5.0
The steel containing so as to satisfy wt% is hot-rolled, and then directly quenched at a cooling rate of 5 to 50 ° C./s to obtain a martensite-based structure, which is 1420 N / mm.
Disclosed is a method for producing a PC steel rod excellent in uniform elongation and high-temperature relaxation characteristics, which is characterized by having a tensile strength of ² or more and is subjected to spot welding followed by tempering energization.

The fourth aspect of the present invention is C: 0.05 to 0.3.
5 wt%, Mn: 0.2-3.0 wt%, Si
And Al of 2.0 wt% ≦ Si + Al ≦ 5.0 wt%
To satisfy Nb: 0.01-
0.1 wt%, Ti: 0.01 to 0.05 wt%, B:
0.0003 to 0.005 wt%, Ni: 0.2 to 1.
0 wt%, Cr: 0.1 to 1.0 wt%, Mo: 0.0
Steel containing at least one of 5 to 0.5 wt% and Cu: 0.2 to 1.0 wt% is hot rolled after hot rolling.
Characteristically, the structure is mainly martensite by direct quenching at a cooling rate of 50 ° C./s, and the tensile strength is 1420 N / mm ² or more. Provided is a method for manufacturing a PC steel rod having excellent relaxation characteristics.

[0019]

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 for enhancing the hardenability and the strength. When directly quenching after hot rolling, C is 0.05 w.
If it is less than t%, the strength level as a PC steel rod cannot be secured. On the other hand, if it exceeds 0.35 wt%, the toughness deteriorates. Therefore, the C content is 0.05 to 0.35 wt.
The range is less than or equal to%.

Si and Al are used as deoxidizing agents, are not only effective for relaxation characteristics, but also contribute greatly 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 spot weldability deteriorates. Therefore, the value of Si + Al is 2.0 to 5.0 wt.
% Range.

Like Mn, Mn is a deoxidizing agent and, like C, is an element required to enhance hardenability and improve strength. However, if the amount is less than 0.2 wt%, the effect is small, while if it exceeds 3.0 wt%, the ductility may decrease. Therefore, the Mn amount is 0.2 to 3.0 w
t%.

Nb, Ti, B, Ni, Cr, Mo, Cu
Each of the elements is an element that contributes to the improvement of hardenability, and if necessary, one or more elements are added. 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, Nb: 0.01 to 0.1 wt
%, Ti: 0.01 to 0.05 wt%, B: 0.000
3 to 0.005 wt%, Ni: 0.2 to 1.0 wt%,
Cr: 0.1-1.0 wt%, Mo: 0.05-0.5
wt%, Cu: 0.2 to 1.0 wt%.

In the present invention, steel having such a composition is hot-rolled and then directly quenched. The heating temperature and finishing temperature for hot rolling are normal operating conditions and are not particularly limited. Preferred conditions are finishing temperature 850-11
00 ° C. If it is lower than 850 ° C, the load during rolling increases and the roll life decreases. If it is higher than 1100 ° C., the austenite grains become coarse.

In the subsequent direct quenching, the cooling rate is 5 to
50 ° C./s. By directly quenching at a cooling rate within this range, a structure mainly containing martensite can be obtained.

P as a material manufactured in this way
When the C steel rod is used for actual prestressed concrete, it may be spot-welded and then tempered and energized for use. In the present invention, it has excellent uniform elongation and high temperature relaxation characteristics even as a raw material or after spot welding and subsequent tempering energization.

[0026]

【Example】

(Example 1) Steel of the present invention having the composition shown in Table 1 (No. 1)
~ 17), comparative steels (No. 18-21) were used as test steels, and a round bar having a diameter of 8 mm was hot-rolled under the conditions shown in the table.
Direct quenching was carried out at a predetermined cooling rate shown in the table, and then, it was drawn out into a rod having a different diameter of 7.1 mm. Tensile test firing and relaxation test.

[0027]

[Table 1]

After that, these as-drawn steel bars were subjected to a tensile test firing and a relaxation test. The uniform elongation was measured by marking each sample with 2d (d is a diameter) and measuring 10d as a gauge length at a distance of 5d or more from the fractured part.

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. Table 2 shows the results of the tensile test including the uniform elongation thus obtained and the results of the normal temperature and high temperature relaxation.

[0030]

[Table 2]

As shown in Table 2, No. It was confirmed that all of the steels of the present invention 1 to 17 had excellent uniform elongation characteristics and relaxation characteristics in the as-rolled and drawn state. On the other hand, the comparative steel No. No. 18 has a large amount of C and is excellent in relaxation characteristics, but the ductility is remarkably reduced due to direct quenching after rolling. No.
No. 19 has a Si + Al content of less than 2.0 wt%,
Uniform elongation was decreasing. On the other hand, No. In No. 20, the cooling rate after hot rolling was insufficient, so that the martensite structure was not obtained and the required strength was not obtained. In addition, No. In No. 21, since the amount of Si + Al exceeds 5 wt% or more, the ferrite fraction becomes too large.
The required strength was not obtained.

(Example 2) Using the test steels in Table 1 above, spot welding was carried out under the welding conditions shown below, and then tempering energization was carried out 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 Example 1.

<Welding conditions> Welding current 2500A Tempering current 2700A Energizing cycle number 2 Pressurizing force 410N Spiral 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.

[0034]

[Table 3]

As shown in Table 3, No. Although all of the steels of the present invention 1 to 17 show a slight decrease in strength and elongation as compared with the results of the material of Example 1, they also have the effect of tempering energization and have excellent uniform elongation and high temperature relaxation characteristics. It was confirmed that

[0036]

As described above, according to the present invention,
There is no need to add steps such as strain imparting and reheating heat treatment,
It is possible to manufacture a PC steel rod having a tensile strength of 1420 N / mm ² or more and 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.

Continued on the front page (72) Inventor Shigeru Mizoguchi 5893 Tamura, Hiratsuka-shi, Kanagawa Prefecture High-frequency refining stock company Shonan Plant (72) Inventor Eiji Yamashita 5983 Tamura, Hiratsuka-shi, Kanagawa Prefecture High-frequency refining stock company Shonan Plant, Inc. (72) Invention Person: Kazushi Nitta 5893 Tamura, Hiratsuka-shi, Kanagawa Prefecture

Claims (4)

[Claims] 1. C: 0.05 to 0.35 wt%, Mn:
0.2 to 3.0 wt%, and Si and Al
5 to 50 [deg.] C./s after hot-rolling steel containing 2.0 wt% ≤ Si + Al ≤ 5.0 wt%
A method for producing a PC steel rod excellent in uniform elongation and high-temperature relaxation characteristics, characterized by having a structure mainly composed of martensite by direct quenching at a cooling rate of 1, and having a tensile strength of 1420 N / mm ² or more. 2. C: 0.05 to 0.35 wt%, Mn:
It contains 0.2 to 3.0 wt% of Si and Al.
0 wt% ≤ Si + Al ≤ 5.0 wt% is contained, and further Nb: 0.01 to 0.1 wt%, T
i: 0.01 to 0.05 wt%, B: 0.0003 to
0.005 wt%, Ni: 0.2-1.0 wt%, C
r: 0.1 to 1.0 wt%, Mo: 0.05 to 0.5 w
t%, Cu: at least 1 out of 0.2 to 1.0 wt%
A steel containing seeds is hot-rolled and then directly quenched at a cooling rate of 5 to 50 ° C./s to form a martensite-based structure having a tensile strength of 1420 N / mm ² or more. , A method for producing a PC steel rod excellent in uniform elongation and high temperature relaxation characteristics. 3. C: 0.05 to 0.35 wt%, Mn:
0.2 to 3.0 wt%, and Si and Al
5 to 50 [deg.] C./s after hot-rolling steel containing 2.0 wt% ≤ Si + Al ≤ 5.0 wt%
The structure is mainly martensite by direct quenching at a cooling rate of 1420 N / mm ² or higher tensile strength, spot welding and subsequent tempering energization Excellent uniform elongation and high temperature relaxation characteristics PC steel rod manufacturing method. 4. C: 0.05 to 0.35 wt%, Mn:
It contains 0.2 to 3.0 wt% of Si and Al.
0 wt% ≤ Si + Al ≤ 5.0 wt% is contained, and further Nb: 0.01 to 0.1 wt%, T
i: 0.01 to 0.05 wt%, B: 0.0003 to
0.005 wt%, Ni: 0.2-1.0 wt%, C
r: 0.1 to 1.0 wt%, Mo: 0.05 to 0.5 w
t%, Cu: at least 1 out of 0.2 to 1.0 wt%
A steel containing seeds is hot-rolled and then directly quenched at a cooling rate of 5 to 50 ° C./s to form a martensite-based structure having a tensile strength of 1420 N / mm ² or more. , A method for producing a PC steel rod excellent in uniform elongation and high-temperature relaxation characteristics, in which spot welding and subsequent tempering current are applied.