JP2002060903A - Bar steel for high strength reinforced concrete - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide bar steel for high strength reinforced concrete producible as hot-rolled. SOLUTION: This bar steel for high strength reinforced concrete has a composition containing, by weight, 0.4 to 0.6% C, 0.02 to 0.7% Si, 1.35 to 2.0% Mn, <=0.03% P, <=0.03% S, 0.09 to 0.2% V, 0.01 to 0.02% N and 0.005 to 0.1% Al, and the balance Fe with inevitable impurities and has excellent mechanical properties such as proof stress, tensile strength, elongation and noncracking at a bending angle of 90 deg. as hot-rolled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel bar for high-strength reinforced concrete, and more particularly to a hot-rolled round bar and a deformed steel bar for reinforced concrete used for reinforcing concrete in a reinforced concrete structure.

[0002]

2. Description of the Related Art Currently, steel bars for reinforced concrete (round bars,
Deformed bar) is a round steel with a proof strength of 235 N / mm ² or more (SR
235), 296N / mm ² or more (SR295) is JI
S. In addition, deformed steel bars have a yield strength of 295 N /
mm ² or more (SD295A) to proof strength 490-625N
/ Mm ² (SD490) up to JIS (JIS G3
112). These steel bars for reinforced concrete are used properly according to the design strength of the structure, but the current strength level requires the use of a large number of steel bars, and the development of steel bars with higher strength from the viewpoint of reducing construction costs. It is presently desired.

[0003] In addition, high-strength deformed steel bars for reinforced concrete used in high-rise reinforced concrete buildings have been standardized. This deformed steel bar has a yield strength of 685 N / mm ² or more (USD 685) and a yield strength of 980 N / mm ² or more (US
D980) and proof stress 785 N / mm ² or more (USD 785) and proof stress 1 for special transverse reinforcing steel.
275 N / mm ² or more. However, among the above deformed steel bars, USD980 satisfying 790 N / mm ²
Is the specified value of the chemical component (C: 0.80 wt% or less, S
i: 2.00 wt% or less, Mn: 2.20 wt% or less,
(Cu: 0.05 wt% or less), the strength is secured by heat treatment such as quenching and tempering. Therefore, it has a problem that it is very expensive from the manufacturing method, and its use range is limited to high-rise reinforced concrete buildings using high-strength concrete that requires high-strength deformed steel bars from structural performance. You.

[0004]

As described above, conventionally, high-strength steel bars have not been obtained from steel bars for reinforced concrete manufactured by hot rolling by adjusting the contents of C and Mn. In addition, in order to obtain a high-strength steel bar from a C-Si-Mn-based steel, heat treatment is required in addition to component adjustment, and the product is extremely expensive, so that it cannot be used except for special purposes. The present invention has been made in view of such circumstances, and provides a high-strength steel bar for reinforced concrete that can be manufactured as hot rolled.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and the component system of a conventional steel bar for reinforced concrete is a C-Si-Mn system. Although it was not obtained, it was very expensive because heat treatment was required to obtain high strength.
V precipitates (V carbides, V nitrides, V carbonitrides) formed by adding V and N to Si-Mn-based components can provide practically effective high strength as hot rolled. It was found.

According to the present invention, C: 0.4-0.6 wt%, S
i: 0.02 to 0.7 wt%, Mn: 1.35 to 2.0
wt%, P: 0.03 wt% or less, S: 0.03 wt%
Hereinafter, V: 0.09 to 0.2 wt%, N: 0.01 to
0.02% wt%, Al: 0.005 to 0.1wt%, proof stress 790N composed of balance Fe and unavoidable impurities
/ Mm ² or more for hot-rolled high-strength reinforced concrete bars. In addition, the present invention provides a method for preparing C: 0.4 to 0.6 wt%,
i: 0.02 to 0.7 wt%, Mn: 1.35 to 2.0
wt%, P: 0.03 wt% or less, S: 0.03 wt%
Hereinafter, V: 0.09 to 0.2 wt%, N: 0.01 to
0.02% wt%, Al: 0.005 to 0.1wt%, Cu: 0.7wt% or less, Ni: 0.5w
t% or less Cr: 0.3 wt% or less, Mo: 0.3 wt%
Below, Nb: 0.1 wt% or less, Ti: 0.05 wt%
Hereinafter, B: one or two or more of 0.0010 wt% or less, and the proof stress 79 consisting of the balance of Fe and unavoidable impurities
It is a hot-rolled high-strength steel bar for reinforced concrete of 0 N / mm ² or more.

In the present invention, C: 0.4 to 0.6 wt.
%, Si: 0.02-0.7 wt%, Mn: 1.35-
2.0 wt%, P: 0.03 wt% or less, S: 0.03
wt% or less, V: 0.09 to 0.2 wt%, N: 0.0
1-0.02% wt%, Al: 0.005-0.1wt
%, Further contains one or more of Ca: 0.005% by weight or less and rare earth elements (La, Ce, Y, etc.): 0.005% or less, and a proof stress of 790 N / It is a hot-rolled high-strength steel bar for reinforced concrete of ² mm or more. Further, the present invention provides a method for preparing C: 0.
4 to 0.6 wt%, Si: 0.02 to 0.7 wt%, M
n: 1.35 to 2.0 wt%, P: 0.03 wt% or less, S: 0.03 wt% or less, V: 0.09 to 0.2 w
t%, N: 0.01 to 0.02% wt%, Al: 0.0
0.05 to 0.1 wt%, and further Cu: 0.7 wt%
Ni: 0.5 wt% or less, Cr: 0.3 wt% or less, Mo: 0.3 wt% or less, Nb: 0.1 wt% or less, Ti: 0.05 wt% or less, B: 0.0010 wt%
% Or less, and Ca: 0.005w
t% or less, rare earth element (La, Ce, Y, etc.): 0.0
It is a hot-rolled high-strength steel bar for reinforced concrete containing at least 790 N / mm ² and containing at least one or two or less of 0.05% and the balance being Fe and unavoidable impurities.

[0008]

In the present invention, C: 0.4 to 0.6 wt%
N: 0.01 to 0.02 wt%, and V:
By containing 0.09 to 0.2 wt%, V precipitates (V nitride, carbide, V carbonitride) are formed. Increase in strength such as proof stress is recognized by the precipitation hardening, and a hot-rolled high-strength reinforced concrete steel bar having a proof strength of 780 N / mm ² or more, an elongation of 10% or more, and a bending angle of 90 ° without cracking as hot rolled is obtained. It is obtained.

The reasons for limiting the components of the present invention are described below. C
Alone has an effect of increasing strength by increasing the pearlite fraction, but further contributes to an increase in proof stress by forming V precipitates of V carbide and V carbonitride.
C: By containing 0.4 wt% or more, the pearlite fraction increases, and the proof stress is improved by the formation of V carbide and V carbonitride, whereby the proof stress of 790 N / mm ² or more can be obtained. C: 0.6
If the content exceeds wt%, ductility decreases, and the required characteristics of elongation and bending angle are not satisfied. C: 0.4 to 0.6 wt
%, Ferrite precipitation amount is small, but V carbide,
The effect of increasing the proof stress is maintained by precipitation hardening of V carbonitride.

N is 30 ppm at a normal converter steel level.
In the present invention, N: 0.01 to 0.02
% Wt. N must be contained in an amount of 0.01 wt% or more in order to increase the strength due to precipitation hardening of V nitride and V carbonitride and to improve the yield strength due to the pinning effect of the precipitate. If N: more than 0.02 wt%, excess N remains as bubbles in the steel ingot at the time of producing the steel soul, and it is difficult to obtain a sound product. Therefore, N is set in the range of 0.01 to 0.02 wt%. . V forms V precipitates of C, N and V nitrides, V carbides, and V carbonitrides, which are the components contained in steel, and increases the strength by precipitation hardening of these V precipitates and the pinning effect of the V precipitates. In order to improve the yield strength, it is necessary to contain V: 0.09% by weight or more, and if it is less than 0.09% by weight, a sufficient effect cannot be obtained. Further, if V exceeds 0.2 wt%, ductility decreases, so V is set in the range of 0.09 to 0.2 wt%.

[0011] Si requires 0.02 wt% or more to increase the strength and deoxidize the molten steel, but if it exceeds 0.7 wt%, the ductility decreases, so that Si: 0.02 to 0.7 wt%
%. Mn is added to secure strength, but its effect is small at less than 1.35 wt%,
If it exceeds wt%, the ductility is reduced, so that Mn is 1.35.
２．０2.0 wt%. Al is usually in the range of 0.005 to 0.1 wt% used as a deoxidizing element.
Limited to the range. P and S are contained in steel as impurity elements, but P: 0.03 wt% and S: 0.03 wt%
If more than, the ductility is impaired, so that P is limited to 0.03 wt% or less and S: 0.03 wt% or less.

Further, according to the requirements of the strength, ductility and joint efficiency of the hot-rolled high-strength reinforced concrete steel bars of the present invention, Cu: 0.7 wt% or less, Ni: 0.5 wt% or less, Cr: 0.3 wt%. % Or less, Mo: 0.3% by weight or less, Nb: 0.1% by weight or less, Ti: 0.05% by weight or less, B: 0.0010% by weight or less. All are added to improve the strength and ductility, but if added beyond the limited range, the ductility is reduced. Also, C
a: 0.005 wt% or less, rare earth element (La, Ce,
Y, etc.): one or more of 0.005 wt% or less are added, and these are added for the purpose of reducing the adverse effect of S contained as an impurity in steel, but the limited range is limited. If added in excess, ductility decreases, so this was made the upper limit.

As a steel to which V is added, a thick steel plate is known. This thick steel plate is used for welding structures such as bridges and crude oil tanks, and the main characteristics required are strength, toughness, and weldability. Therefore, the C content is suppressed to as low as 0.20 wt% or less, and the strength (tensile strength) is about 490 to 590 N / mm ² . In recent years, in the field of angle iron, the strength (tensile strength) to which V is added 7
An angle iron of 90 N / mm ² was developed. This steel was developed for power transmission towers, and the main characteristics required are strength,
It is tough and hot-dip galvanized cracking. Therefore, this steel also has a C content of 0.22% by weight or less and a tensile strength of 6%.
90 to 840 N / mm ² and proof strength of 520 N / mm 2 or more. As described above, all steels utilizing V precipitates have a low C content. This is because V precipitates precipitate in ferrite and contribute to an increase in proof stress. On the other hand, in the hot-rolled high-strength reinforced concrete steel bars of the present invention, the C content is as high as 0.4 to 0.6 wt%. Conventionally, it has been thought that in such a high C content range, the pearlite fraction becomes high (the amount of ferrite is small), and strengthening by V precipitates cannot be expected. The present invention has been made based on the finding that even with steel having such a high C content, the proof stress can be increased by appropriately regulating the V and N contents.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The high-strength steel bars for reinforced concrete according to the present invention are round bars and deformed bars manufactured by hot rolling, and are used for reinforcing concrete of reinforced concrete structures. The steel bar for high-strength reinforced concrete of the present invention has a yield strength of 780 N / mm ² or more and a tensile strength of 112.
0N / mm ² or more, elongation more than 10%, the bending angle by having properties without such cracks in 90 °, (1) can be reduced necessary cross-sectional area of the steel bar to withstand the same load, reinforced concrete structures by decreasing the rod diameter Weight of the steel bar occupied by the steel bar can be reduced. (2) It is possible to reduce the number of bar arrangements of steel bars that can withstand the same load, and to reduce the man-hours for the arrangement of the bars and the construction cost due to the reduction of the time for joining the steel bars. Further, it can meet the demand for high-strength quality of steel bars for reinforced concrete, and can respond to expansion of application fields such as types of structures, design methods, construction methods, and enlargement of structures.

[0015]

EXAMPLES Examples of the present invention are shown in Tables 1 and 2. Table 1 shows the chemical components (wt%) of the steel of the present invention and the comparative steel, and Table 2 shows the production conditions, proof stress (N / mm ² ), tensile strength (N / mm ² ), and elongation. Tensile test result, 90
1 shows the results of a bending test based on the presence or absence of cracks during bending. As is clear from Tables 1 and 2, within the composition range of the present invention, the hot-rolled high-strength steel bars for reinforced concrete of No. 1 to No. 10 of the present invention have a yield strength of 780 N /
mm ² or more, the tensile strength of 1120N / mm ² or more, the elongation 1
A test result of 0% or more and no crack at a bending angle of 90 ° was obtained.

On the other hand, the comparative steels No. 11 to No. 1
In No. 4, C (0.4% or less), V, N, and Al are out of the range of the present invention. This was low in yield strength and tensile strength, and a high strength steel bar could not be obtained. No. 15 of the comparative steel is C
(0.6% or more), V, N, and Al are out of the range of the present invention and are heat-treated after hot rolling. They have high proof stress and tensile strength, but have desired properties by elongation and bending. I couldn't.
In Comparative Steel No. 16, N was out of the range of the present invention, the yield strength and tensile strength were low, and a high-strength steel bar was not obtained. In addition, excess N remains as bubbles in the steel ingot during the production of the steel soul, making it difficult to obtain a sound product.

[Table 1]

[Table 2]

[0017]

As described above, according to the present invention,
A high-strength steel bar for reinforced concrete having excellent mechanical properties such as proof stress, tensile strength, elongation, and no cracking at a bending angle of 90 ° is manufactured by hot rolling. It is possible to reduce the weight due to the reduction in the number of bars, and to reduce the number of bars arranged by increasing the yield strength. In addition, the joining time of the steel bars can be shortened, and the effect of reducing the man-hour for reinforcing bars and the construction cost can be achieved.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Ken Kanaya 3-4-5 Toyosu, Koto-ku, Tokyo Inside Tomoe Giken (72) Inventor Takashi Shimanuki 3-4.5 Toyosu Toyosu, Koto-ku, Tokyo Shares Company Tomoe Giken

Claims (4)

[Claims] 1. C: 0.4 to 0.6 wt%, Si: 0.
02-0.7 wt%, Mn: 1.35-2.0 wt%,
P: 0.03 wt% or less, S: 0.03 wt% or less,
V: 0.09 to 0.2 wt%, N: 0.01 to 0.02
% Wt%, Al: 0.005 to 0.1 wt%, proof stress 790 N / mm ² consisting of balance Fe and inevitable impurities
The above hot-rolled high-strength steel bars for reinforced concrete. 2. C: 0.4 to 0.6 wt%, Si: 0.
02-0.7 wt%, Mn: 1.35-2.0 wt%,
P: 0.03 wt% or less, S: 0.03 wt% or less,
V: 0.09 to 0.2 wt%, N: 0.01 to 0.02
% Wt%, Al: 0.005 to 0.1 wt%.
Furthermore, Cu: 0.7 wt% or less, Ni: 0.5 wt% or less
Cr: 0.3 wt% or less, Mo: 0.3 wt% or less, N
b: 0.1 wt% or less, Ti: 0.05 wt% or less,
B: Including one or more of 0.0010 wt% or less
, Proof stress 790 N / consisting of Fe and unavoidable impurities
mm ²The above hot-rolled high-strength steel bars for reinforced concrete. 3. C: 0.4 to 0.6 wt%, Si: 0.1 to 0.3 wt%.
02-0.7 wt%, Mn: 1.35-2.0 wt%,
P: 0.03 wt% or less, S: 0.03 wt% or less,
V: 0.09 to 0.2 wt%, N: 0.01 to 0.02
% Wt%, Al: 0.005 to 0.1 wt%, Ca: 0.005 wt% or less, rare earth element: 0.0
A hot-rolled high-strength reinforced concrete steel bar containing not less than one or two or more kinds of not less than 05%, and having a proof strength of 790 N / mm ² or more, the balance being Fe and unavoidable impurities. 4. C: 0.4 to 0.6 wt%, Si: 0.
02-0.7 wt%, Mn: 1.35-2.0 wt%,
P: 0.03 wt% or less, S: 0.03 wt% or less,
V: 0.09 to 0.2 wt%, N: 0.01 to 0.02
% Wt%, Al: 0.005 to 0.1 wt%, Cu: 0.7 wt% or less, Ni: 0.5 wt% or less, Cr: 0.3 wt% or less, Mo: 0.3 wt% or less, N
b: 0.1 wt% or less, Ti: 0.05 wt% or less,
B: one or more of 0.0010 wt% or less, Ca: 0.005 wt% or less, rare earth element: 0.00
A steel bar for hot-rolled high-strength reinforced concrete containing at least 790 N / mm ² and containing not less than 5% of one or more kinds and the balance consisting of Fe and unavoidable impurities.