JPS5877554A - Salt resistant steel bar for reinforced concrete - Google Patents

Abstract

PURPOSE:To obtain an inexpensive steel bar for reinforced concrete with high resistance to corrosion due to salt in concrete by regulating the S content to an especially low value and by adding prescribed percentages of Cr, C, Si, Mn and P. CONSTITUTION:This salt resistant steel bar for reinforced concrete consists of, by weight, <=0.035% C, <=1.0% Si, <=2.0% Mn, <=0.050% P, <=0.005% S in particular, 0.1-3.0% Cr and the balance Fe with inevitable impurities. The steel bar has superior resistance to corrosion due to salt in concrete. Accordingly, when it is used in a reinforced concrete structure or the like in coastal or oceanic environment or environment along a road over which antifreezing salt is spread, the safety and durability of the structure are remarkably enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to steel bars for reinforcing bars used in reinforced concrete structures, particularly for reinforced concrete structures in coastal or marine environments such as port facilities, offshore plant homes, submarine resource excavation equipment, and offshore oil storage tanks. It is also suitable for use as reinforcing bars in reinforced concrete structures that are exposed to corrosive environments due to salt, such as reinforced concrete structures along roads that have been sprayed with antifreeze salt, or even reinforced concrete structures constructed using sea sand or seawater. This relates to steel bars for reinforced concrete.

As is well known, the reinforcing bars in reinforced concrete structures are PI (
The surface is protected by a dense oxidized layer called a passive film, which is covered with strong alkaline concrete of about 10 to 13, and is usually considered to be just one side dish. However, in the case of concrete structures built in coastal or marine environments or along roads sprayed with antifreeze salt, as mentioned above, and reinforced concrete structures constructed using sea sand or seawater, the salt content in the concrete In this case, the passive film on the surface of the reinforcing bars in the concrete is destroyed by the salt, and corrosion progresses significantly. If corrosion progresses in this way, the generated rust reduces the adhesion between the reinforcing bars and the concrete, reducing the strength of the reinforced concrete structure and causing peeling of the concrete.

Pitting corrosion of reinforcing steel with still concrete cracks 1,
It has a notch effect on structures, and there is a risk of structural failure due to excessive stress caused by typhoons, earthquakes, etc. As described above, corrosion of reinforcing bars due to salt significantly reduces the safety and durability of structures, and therefore, there has been a strong desire to establish corrosion protection technology for reinforcing bars against salt corrosion.

Conventional anti-corrosion measures for this glaze include improving the construction specifications of the concrete itself, such as increasing the thickness of the concrete cover over the reinforcing bars, adding inhibitors to the concrete to prevent cracking, and adding polymer cement to the concrete. There are known methods to prevent the salt concentration of concrete near the surface of reinforcing bars from increasing by applying a surface coating, etc., and in order to prevent corrosion of the broken reinforcing bars themselves, the reinforcing bars may be coated with ZN Meggi or He. It is also known to apply epoxy powder coating to the surface of plated υ or reinforcing bars. However, it is difficult to obtain a sufficient corrosion protection effect with any of these methods, and depending on the trench method, there is also the problem of increasing construction costs. Therefore, adjusting the steel composition of reinforcing bars is considered to be the most promising way to prevent salt-induced corrosion.

By the way, conventional low alloy steels that have been given corrosion resistance by adjusting their composition include P, Cu, Ni, and Cr.
Weathering-resistant steels with additions of Cr, Cu, Mo, etc., and sulfuric acid-resistant steels with additions of Cu, Ni, etc., are known. However, the environment in which these steel materials are applied is a neutral or acidic environment with a pH of 8 or less, and the corrosion mechanism and the action of added alloying elements are thought to be different from the environment in strongly alkaline concrete. steel, seawater-resistant steel, and sulfuric acid-resistant steel.
Even if component adjustment using IU is applied to reinforcing bars in concrete, it is difficult to impart salt resistance to the reinforcing bars in concrete.

This invention was made in view of the above circumstances, and it is a reinforced concrete that has a composition different from that of conventional corrosion-resistant steel, and has a 714 composition, which provides good corrosion resistance against salt corrosion in concrete and is also inexpensive. The first objective is to provide steel bars for industrial use.

In other words, this invention was made as a result of a detailed study of the mechanism and progress of salt corrosion of reinforcing bars in concrete. Conch IJ with multiple needles
-1- We simulated the corrosion situation of reinforcing bars in structures in a laboratory setting using NaC-g saturated Ca (OH) 2 melting at JfJ. As a result of a detailed cross-sectional investigation into the influence of Yohosu alloy components, we found that by significantly reducing the S content in the steel compared to the S content of conventional ordinary steel, and adding Cr in the low S region, It is possible to reduce the starting points of corrosion and strengthen the passive film to improve salt resistance, and furthermore,
.

By adding Cu and Ni, the above 11νI
It was discovered that the salt effect (5) could be further improved, and this invention was made.

To explain the above findings in more detail, hot-rolled materials used as ordinary steel bars for reinforced concrete have a hardness of 8.0.050% or more according to the JIS standard, and have poor hot workability and toughness. The i-contact strength is reduced due to the low 1 of The regulations are stipulated from the aspects of steel manufacturing, hot working, bath welding, etc., and do not take into account salt corrosion of reinforcing bars in concrete structures.

Since the surrounding concrete is strongly alkaline, reinforcing bars in concrete structures normally form a passive film as mentioned above and are almost corroded, but they are used in coastal/marine environments and along roads sprayed with antifreeze salt. 5 for construction using sea sand or sea water due to environmental concerns or deterioration of fine aggregate or water conditions.
In contrast, the salt concentration of concrete in reinforced concrete structures (6) increases,
As a result, the passive structure on the surface of the reinforcing bars is easily destroyed, and corrosion progresses markedly, especially in concrete containing NaC (3VC equivalent, 01% to 01% AK). As a result of simulating the actual environment in delicious concrete in a swamp containing NaCe and Ca (OII), we investigated in detail the corrosion occurrence of reinforcing bars due to salt. It was discovered that it occurs from substances, especially sulfide-based nonmetallic inclusions such as Mn8, and further investigation revealed that
When S exceeds 0005%, the number of starting points for eclipses increases,
Increased corrosion area and pitting 1. In other words, the S content is lower than the content 1i (003 to (101 black) of ordinary steel).
It has been found that it is necessary to limit the content to 1.005% or more for resistance to 1. Similarly to the above, the actual environment in concrete with high salt concentration was investigated.
As a result of a detailed investigation of the influence of Jj Yobazu alloy components on salt corrosion of reinforcing bars by simulating with oH)2 solution, it was found that Cr (1) 14 It has been found that this method has a remarkable effect of improving salt resistance by strengthening the passive film and suppressing the occurrence of rust and pitting corrosion. Furthermore, in addition to adding 5lr) of Cr to the low S region as described above, Al1 and Ni were added.

By adding more than 18 ft.02s of Cu, the salt resistance effect increases dramatically, and even in the cracks of the concrete itself, it becomes a non-resistant material that is resistant to the intrusion of corrosive substances such as H2O, 02, and Cβ. They discovered that a functional film is formed.

Therefore, the steel bar for reinforced concrete of this invention has excellent salt resistance by controlling the S content in the steel to 0.005% or less and adding Cr at the same time. In addition, two or more types of Ni are added to further improve the salt tolerance effect.

Specifically, the steel bar for reinforced concrete according to the first invention has C035 or more 1, S+1.0% or less, and Mn 2
．． O% or more 1, Po, 050% or more, SO, 005%
Hereinafter, it is characterized in that it contains 01 to 30% Cr, and the remainder consists of Fe and inevitable impurities. The steel bar for reinforced concrete according to the second invention contains, in addition to the above-mentioned components, one selected from Ag, Cu, and Ni, or 1.0 or more of 24ili or more.
It is added in a range of 0.01 to 3.0% in total.

Next, the reinforced concrete 111 steel bar 1 (c,
Regarding the behavior of each component and the reason for limiting the components,
explain.

C is an element that affects the strength, toughness, weldability, and normal surface/monocorrosion properties of steel.If it is 0.3% or more, the effect is small, but if it exceeds 0.3%, Reduces toughness, weldability and general corrosion resistance.

Therefore, the lower limit of C was set at 03%.

It has a deoxidizing effect on Si, and it is preferable to have some degree of swelling in order to improve normal corrosion resistance, but the Si content is lower than 10. ! If <-t'+, it will have a negative effect on workability and weldability, so the upper limit of Si is t';
It was set at 10.

Mn has a deoxidizing effect and improves the strength 1G as well as hot workability and weldability9). However, if Mn is less than 0.2%, these effects are small, so it is desirable to contain Mn in an amount of 0.2% or more.

On the other hand, even if Mn exceeds 20%, the effect of improving hot workability and bath weldability is not so great compared to the amount added, so the upper limit was set at 20% from the viewpoint of economic cost.

As mentioned above, S is a harmful element to salt corrosion in conc IJ-1-, and salt resistance can be improved by reducing the S content. SO,0
Below 0.05%, the effect of improving salt tolerance is remarkable;
%, harmful sulfide-based nonmetallic inclusions will be present in large quantities in the steel, impeding salt resistance, so the upper limit of S is set to O.
, OO5%.

Salt resistance is improved if a large amount of P is added, but hot workability, toughness, and weldability are reduced if P is added in excess, so the upper limit was set at 0.05%.

When added in the low S range, C synergistically increases the salt resistance effect, but the effect is small below 01%, so the lower limit was set at 01%. In addition, if the amount of Cr added exceeds 30, the hot workability (10) and toughness will decrease, and the salt resistance -1 effect will not be improved compared to the amount added, resulting in higher costs. The upper limit of Cr was set to 30%.

Ag, Cu, Ni combined with Cr in the low S region
When added alone or in combination, Knee C strengthens the passive film on the surface of the reinforcing steel, reduces local corrosion in cracked areas of concrete, and improves salt resistance to 1. <Direction -1. However, 4□5-C for both single addition and combined addition.
If the amount is less than 01%, the surface j1 effect is not significant, and therefore the limit of the total addition amount is set to 01φ. - If the amount of 〇 added to the force exceeds 10 inches, hot processing will be 1/1. J.
5 and the addition of Cu to lower the toughness and -111 or +
1) If it exceeds 1%, it will increase the general eating quality, but it will cause surface defects and scratches during hot rolling.
If tooth σ no cannon/Jll iri exceeds 10chi, it will be compared to the 1-control propensity effect and become 17"su l-sho, so it will be added alone,
The upper limit of each addition 11 is taken as 10% for the compound addition case r1, and Ag, Cu,
In the case of composite addition of Ni, if the synergistic effect on Cr addition at low Siil't'a is so large that the talkability improvement effect is not so large compared to that for cooling, the total addition will be expensive. The upper limit of the amount was set to 30.J, 3 Ae,
Cu.

By adding N1 together with Cr addition in the low S range of SO, 0.005% or more, the effect of improving copper salt property can be obtained for the first time, and when the S content is high, Even if it is added, the l1j4 salinity improvement effect cannot be expected at all.

Below are 16 practical examples of the present invention and comparative examples.

EXAMPLES Sample numbers 7 to 13 in Table 1 were melted and forged for each copper electrode within the non-inventive composition range, and then joined to a general process fillet, drawn, and A steel bar with a diameter of D13 was manufactured. In this way, the steel bar for reinforcing bars obtained by
(Mountain sand) 38%, salt concentration in concrete (NaC conversion) 02, diameter 50mm, length 300m++
Concrete l) - Embedded in the center of the concrete, underwater at a depth of 4 m 4
．． 5 and a seawater spray zone for 5 years, and after collecting the test pieces, the corrosion area rate and maximum pitting depth of the reinforcing bars were measured. The results are also shown in Table 1.

Comparative Example For each steel type shown in Sample Nos. 1 to 6 in Table 1, which are outside the range of A and 11 of the present invention, steel bars for reinforcing bars were prepared in the same manner as above.
A similar corrosion test was conducted by pushing the sample into concrete in the same manner as described above. The results are shown in the first column.

(1:3) According to the corrosion test results shown in Table 1, the corrosion of reinforcing bars is more severe in the seawater splash zone than in seawater, but in any environment, 0.005% S in steel is used. It is clear that the salt resistance can be significantly improved by adding Cr along with the following restrictions.

Furthermore, by adding one or two or more of Ae, Cu, and Ni in addition to the addition of Cr, which is in the low S range of SO, 005 Article 1, a synergistic effect is exhibited, resulting in a dramatic increase in J pyrolysis resistance. It is clear that it grows naturally. Comparative Example 3 is one in which -CCr is added to the S region, and Comparative Examples 4 to 6 are added in the high S region e (in addition to the addition of C [Cu r
Although Nr + ke k t4> is added, the increase in salt resistance is small in both cases, and therefore the addition of Cr and the addition of Cr and Cu, Ni, and Ae are effective in the low S region. was confirmed.

As is clear from the above description, the steel bar for reinforced concrete of the present invention has anti-corrosion properties that are resistant to corrosion caused by salt in concrete, and therefore, it can be used in coastal areas as well as in oceans and seas. Reinforced concrete in the environment along the sprayed road (15) Structures, as well as sea sand and dσ water 1) I・HaI 1. −
t' lAl soil] - 1 "f+" for use in concrete structures, etc., significantly improves the safety and durability of structures by CJI et al.
, < 1714-1.

Applicant: Kawasaki Steel Corporation (16)

Claims (2)

[Claims] (1) CO. 35% (weight%, same below) or less, Si1
．． 0% or less, Mn 2.0% or less, P 0,050% or less,
A copper salt steel bar for reinforced concrete, characterized in that it contains 80005% or less, 01 to 30% Cr, and the remainder consists of Fe and inevitable impurities. (2) CO, 35% or more = T, 8410% or more 1, Mn
2.0 inches or less, P O, 050% or more 1, S O, 005
% or less, containing Cr 0.1 to 30%M,
Aβ. It is characterized by containing one or more selected from Cu and Ni in an amount of 10% or less each, with a total amount of 01 to 3.0%, and the remainder consisting of Fe and unavoidable impurities. Salt-resistant steel bars for reinforced concrete.