JPH02240236A - Salt damage-resistant pc steel bar - Google Patents

Abstract

PURPOSE:To obtain the salt damage-resistant PC steel bar having excellent relaxation properties, weldability and mechanical characteristics as well as having excellent delayed fracture characteristics by specifying the compsn. constituted of C, Si, Mn, P, S, Ni and Fe. CONSTITUTION:The salt damage resistant PC steel bar contains, by weight, 0.2 to 0.4% C, 0.2 to 2.0% Si, 0.2 to 1.5% Mn, <=0.020% P, <=0.005% S and 3 to 5% Ni, furthermore contains, at need, one or both of 0.05 to 0.5% Cu and 0.03 to 0.5% W and/or 0.0003 to 0.0050% B and the balance Fe with inevitable impurities, which has improved delayed fracture characteristics and salt resistance while maintaining excellent relaxation properties, weldability and mechanical characteristics similar to those of a conventional PC steel bar.

Description

[Detailed description of the invention] "Purpose of invention" (Industrial application field) The present invention relates to a salt-resistant PC steel bar.

(Prior art) In recent years, cracking and deterioration in concrete buildings in coastal areas and reinforced concrete buildings using sea sand has become a problem, but this is caused by the salinity of sea salt particles and the salt in sea sand. This occurs due to corrosion of reinforcing bars buried in concrete, and to prevent this,
Various methods have already been developed to improve salt resistance by controlling the chemical composition of reinforcing bars themselves.

For example, in Japanese Patent Publication No. 55-22546, by adding Cu and W at the same time, and in Japanese Patent Publication No. 57-480,
No. 54 proposes to improve salt resistance by adding a large amount of Ni, and JP-A-63-161120 proposes to add a large amount of Cr to improve salt resistance.

Although the above-mentioned proposals are all related to reinforcing bars, PC steel bars are also used as reinforcing materials for concrete buildings, just like these reinforcing bars. However, in this PC steel bar, corrosion due to the PC ice ball sea salt particles and corrosion due to the use of sea sand in the PC pile ball are unavoidable, similar to the above-mentioned reinforcing bars, and the same problems as those caused by reinforcing bars are occurring. .

In addition, reinforcing bars are used as rolled and have relatively low strength, so they have delayed fracture properties and relaxation properties (JIS G
According to 8.2 of 3109), etc., consideration is not required. On the other hand, PC steel bars are manufactured using hot-rolled materials by stretching, drawing, heat treatment, or a combination thereof.

Incidentally, as an example of an attempt to improve the salt resistance of such a PC steel bar, there can be cited Japanese Patent Application Laid-open No. 83752/1983.

(Problem to be solved by the invention) The conventional PC steel bars as described above are mainly made of carbon steel, and although there are some steels containing a large amount of Si + Cr, Mn, etc., salt resistance is not given much consideration. It has not been.

In addition, even if the desired salt resistance is achieved by increasing the strength, other delayed fracture characteristics, relaxation characteristics,
Other properties such as weldability and mechanical properties are not necessarily sufficient. In addition, what is shown in the above-mentioned Japanese Patent Application Laid-Open No. 58-83752 is Ca, RE! The aim is to reduce sulfide in steel and change its properties by adding H alone or in combination, thereby improving salt resistance, but at present it is difficult to stabilize the yield of Ca. , there are many manufacturing problems.

The present invention is a salt-resistant PC! PC steel bars have improved delayed fracture properties and salt resistance while maintaining the same glue laxation properties, weldability, and mechanical properties as conventional PC steel bars.
The aim is to provide steel rods.

"Structure of the Invention" (Means for Solving the Problems) As a result of intensive research to solve the above problems, the present inventors have discovered that the salt resistance and delayed fracture of steel that has been heat treated and has a tempered martensitic structure has been improved. We have discovered a component system that improves properties, weldability, relaxation properties and mechanical properties.

That is, the above problem is solved by (IIC: 0.2 to 0.4% by weight, Si: 0.2 to 2% by weight).
0% by weight, gate n: 0.2~:5% by weight, P≦0.0
20% by weight.

Salt-resistant PC with excellent delayed fracture properties, characterized by containing S≦0.005% by weight, Ni: 3-5% by weight, and the balance consisting of Fe and inevitable impurities; (2) C: 0
．． 2 to 0.4% by weight, Si: 0.2 to 2.0% by weight,
Mn: 0.2 to 5% by weight, P≦0.020% by weight.

Contains S≦0.005% by weight, Ni: 3 to 5% by weight, Cu: 0.05 to 0.5% by weight, W: 0.03
A salt-resistant PC steel bar with excellent delayed fracture properties, characterized by containing one or more of ~0.5% by weight and the remainder consisting of Fe and unavoidable impurities; (3) C: 0.2~ 0.4% by weight, Si: 0.2-2.
0% by weight, Mn: 0.2~:5% by weight, P≦0.0
20% by weight.

S≦0.005% by weight, Ni: 3 to 5% by weight, B: 0
．． 0003 to 0.0050% by weight, with the remainder being Fe.
Salt-resistant PC steel bar with excellent delayed fracture properties, characterized by consisting of carbon dioxide and unavoidable impurities; (4) C: 0.2~
0.4% by weight, Si: 0.2-2.0% by weight 9M port: 0
．． 2~: 5% by weight, P≦0.020% by weight S≦o, oo
s weight %, N1 = 3 to 5 weight %, Cu: 0.05 to 0.
5% by weight, W: one or more of 0.03 to 0.5% by weight, and B: 0.0003 to 0.0050% by weight, with the remainder consisting of Fe and inevitable impurities. We have found that the problem can be solved by using a salt-resistant PC steel bar with excellent delayed fracture properties.

(Function) The reasons for limiting the components of the PCG rod according to the present invention in terms of weight % (hereinafter simply referred to as %) are as follows.

C is an element necessary to improve hardenability and increase strength, and in order to ensure the strength level as a PC steel bar,
0.2% or more is required. However, if it exceeds 0.4%, the spot weldability will deteriorate, so the upper limit is set at 0.4%.

Since Si is used as a deoxidizing agent and is effective for delayed fracture characteristics and relaxation characteristics, 0.2
% or more is required, and it is desirable to add a large amount, but 2.0%
If the content exceeds 2.0%, the ductility of the steel deteriorates, so the upper limit is set at 2.0%.

Mn is a deoxidizing agent like Si, and like C, it is an element necessary for improving hardenability and strength, so it is 0.2
% or more is required. However, if it exceeds 5%, the ductility deteriorates, so the upper limit is set at 5%.

P is an element that cannot be avoided as an impurity element, but since it deteriorates delayed fracture characteristics, it is kept at 0.020% or less.

Since S deteriorates salt resistance, it is desirable to reduce it as much as possible. In the present invention, it is set to 0.005% or less.

Ni is an important element in the present invention, and not only has an effect on salt resistance but also contributes to improving delayed fracture characteristics.

This effect cannot be fully expected with a content of less than 3%, and a content of more than 5% is disadvantageous for economic reasons.

Therefore, the lower limit is set to 3% and the upper limit is set to 5%.

Cu and W are elements that can improve delayed fracture characteristics without deteriorating salt resistance, but if they are added in large amounts, they are economically disadvantageous. Therefore, the lower limit of Cu is 0.05% and the upper limit is 0.5%, and the lower limit of W is 0.03% and the upper limit is 0.5%.

B improves hardenability and delayed fracture properties, but if it is less than 0.0003%, the effect is not obvious, and if it exceeds 0.0050%, it actually reduces hardenability, so the lower limit is set to 0. .0003%, and the upper limit is 0.0050%. In addition, when adding B, Ti is usually added to improve the hardenability of B, but this is to fix N in the steel, and for the B content in the above range, 0.02
Appropriately is around 0% Ti. It is also effective to add one or more of Zr and Nb, which have the same effect as Ti.

(Example) Steel having the components shown in Table 1 below was rolled into a round bar with a diameter of 9.5 u, drawn into a round bar with a diameter of 9.0 mm, and then quenched and tempered by high frequency heating. Hardening is 930-10
Tempering was carried out at an optimum temperature of 20° C., aiming at a tensile strength of 150 kgf/+n”. It is clear that the heat treatment is not limited to high frequency only.

Mechanical properties, salt resistance, and
Test results for delayed fracture properties, relaxation properties, and weldability are shown in Table 2 below.

In the tensile test, the heat-treated material was stretched at a gage length of 72 cranes.

The salt tolerance test was conducted by the autoclave method shown in FIG. The test process is as shown below.

■ Fine aggregate type The test material is poured into concrete containing 10.5% salt (NaC1), and the cured test specimen is inserted into an autoclave and sealed.

■ As shown in Figure 1, approximately 18 lbs.
A temperature of 0°C and a pressure of 10 kgf/am'' was reached, maintained at this condition for 5 hours, and then allowed to cool naturally.

■ Remove the test specimen approximately 24 hours after starting the autoclave test.

■ Immerse in water at 20℃ for about 24 hours.

■ Place in the autoclave again and perform operations ■ and ■.

After the test, the test materials were taken out of the concrete, the corrosion loss was measured, and salt resistance was evaluated.

The delayed fracture test was conducted by applying a stress of 80% of the tensile strength to the sample material and immersing it in a 20% NH48CN solution heated to 50° C., and evaluation was performed based on the time to fracture.

The relaxation test was conducted and evaluated according to the method of JIS G 3109.

The high-temperature relaxation test was carried out in accordance with the method described in Building Letter, No. 28, 1971, page 3, ``Joint test/result report on relaxation of PCM rods and steel wires at high temperatures.

These conditions are as shown in FIG.

In the weldability test, welding current: 250OA, number of current cycles: 2. Mating material: A 3.2u round bar of SWRM8 was used, and after cross welding, a tensile test was conducted to determine the strength,
○ if the elongation satisfies the JIS G 3109 standard
It was marked as a mark.

That is, according to Table 2, the mechanical properties, relaxation properties, and weldability of the steel of the present invention are equivalent to those of the conventional steel,
It satisfies the characteristics as a PC steel bar. On the other hand, its salt resistance and delayed fracture properties are comparable to conventional steel.

It was found to be superior to comparative steels.

"Effects of the Invention" As explained above, according to the present invention, it has excellent corrosion resistance against salt in concrete and salt of sea salt particles, and has delayed fracture characteristics.

This invention is industrially very effective because a PC steel bar can be obtained that has excellent properties in terms of relaxation properties, weldability, and mechanical properties.

[Brief explanation of drawings]

The drawings show the test conditions for the PC steel bar described in the Examples of the present application, in which Figure 1 shows the test conditions of the autoclave method for evaluating salt resistance, and Figure 2 shows the conditions of the high temperature relaxation test. are shown respectively.

Claims (4)

[Claims] (1) C: 0.2-0.4% by weight, Si: 0.2-2.
0% by weight, Mn: 0.2-1.5% by weight, P≦0.02
0% by weight, S≦0.005% by weight, Ni: 3-5% by weight
A salt-resistant PC steel bar with excellent delayed fracture properties, characterized in that the balance consists of Fe and unavoidable impurities. (2) C: 0.2-0.4% by weight, Si: 0.2-2.
0% by weight, Mn: 0.2-1.5% by weight, P≦0.02
0% by weight, S≦0.005% by weight, Ni: 3-5% by weight
Contains Cu: 0.05 to 0.5% by weight, W
: A salt-resistant PC steel bar with excellent delayed fracture properties, characterized by containing one or more of the following: 0.03 to 0.5% by weight, with the remainder consisting of Fe and unavoidable impurities. (3) C: 0.2-0.4% by weight, Si: 0.2-2.
0% by weight, Mn: 0.2-1.5% by weight, P≦0.02
0% by weight, S≦0.005% by weight, Ni: 3-5% by weight
contains B: 0.0003 to 0.0050% by weight,
A salt-resistant PC steel bar with excellent delayed fracture properties, characterized in that the remainder consists of Fe and unavoidable impurities. (4) C: 0.2-0.4% by weight, Si: 0.2-2.
0% by weight, Mn: 0.2-1.5% by weight, P≦0.02
0% by weight, S≦0.005% by weight, Ni: 3-5% by weight
Cu: 0.05-0.5% by weight, W: 0.03-0.
One or more of 5% by weight and B: 0.0003 to 0.00
Salt-resistant P with excellent delayed fracture properties, characterized by containing 50% by weight and the remainder consisting of Fe and unavoidable impurities.
C steel bar.