JPS6092447A - Iron reinforcing rod for concrete with superior corrosion resistance - Google Patents

Abstract

PURPOSE:To obtain an iron reinforcing rod showing superior corrosion resistance even in concrete contg. chloride, etc. by adding V, P, Zr, Sn, Y, Al, N or Ti to a steel having a restricted S content as the material of a corrosion resistant iron reinforcing rod having a regulated composition or by further adding Cu. CONSTITUTION:This iron reinforcing rod consists of, by weight, 0.001-0.300% C, <=1.0% Si, <=1.7% Mn, 0.0001-0.0100% S, one or more among 0.02-0.50% V, <0.05-0.15% P, 0.02-0.80% Zr, 0.02-0.60% Sn, 0.01-0.30% Y, 0.02-1.00% Al, 0.01-0.05% N and 0.02-0.30% Ti and the balance Fe or further contains 0.03- 0.60% Cu. The rod shows extremely superior corrosion resistance in concrete contg. chloride, etc., and it is relatively inexpensive.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to concrete bars and steel bars used in structures.
The present invention relates to reinforcing bars such as shaped steel or steel wire, particularly reinforcing bars for concrete that exhibit extremely good corrosion resistance even in corrosive environments caused by chlorides.

In general, the reinforcing bars in a reinforced concrete IJ-to structure are covered with concrete that exhibits an alkalinity of about 1113 in normal conditions, so they are passivated and corrosion does not occur.

However, in recent years, as the supply shortage of sea sand, a material for concrete, has become more serious, and the amount of sea sand used as a substitute has increased, the chlorides contained in this sea sand have weakened the reinforcing steel in concrete. Concerns have grown that reinforced concrete structures will corrode and reduce their useful life. In other words, if chlorine ions are present in concrete, the passive coating on the reinforcing bars will break and corrosion will progress, and the rust that occurs will reduce the adhesion between the reinforcing bars and concrete, resulting in a decrease in the strength of concrete structures, cracks, etc.
Otherwise, it may cause peeling.

Of course, this is not limited to concrete structures mixed with sea sand, but also common to reinforced concrete structures used in marine environments or coastal areas affected by seawater, or reinforced concrete structures used in other chloride environments. It was also a problem.

Furthermore, in the long term, concrete becomes neutralized and crumbles due to the action of carbon dioxide gas contained in the air, so preventing corrosion of reinforcing bars has been an extremely difficult problem from this point of view as well.

Conventionally, corrosion prevention measures for concrete reinforcing bars include: ■ adding inhibitors (sodium nitrate, etc.) to the concrete to control the environment, ■ surface treatments for reinforcing bars (surface painting, epoxy resin coating, galvanizing, etc.).
However, the inhibitor addition method shown in item 0 above allows rainwater and seawater to seep into the concrete over time, so this prevents the inhibitor from being contained in the concrete. However, there is a problem in that the anti-corrosion effect is deteriorated as a result of diffusion of the inhibitor out of the system, making it extremely difficult to maintain an effective concentration as an inhibitor. Of the treatment methods, the effect of surface painting is not sustained over a long period of time, and the method of coating with epoxy resin leaves the welded area bare, making it impossible to avoid corrosion from that area. Aluminum plating is a very effective method, but it is very effective.
In the long term, it could not be said to be a complete anti-corrosion measure, and furthermore, epoxy resin coating and metal plating had the problem of extremely high processing costs, so neither method was satisfactory.

For this reason, we have recently adjusted the ingredients of reinforcing bars to increase their corrosion resistance to two to three times that of conventional reinforcing bars, thereby minimizing the amount of rust that occurs and reducing the strength of concrete structures, thereby extending their lifespan. (For example, Japanese Patent Application Laid-Open No. 5.6-152944, Japanese Patent Laid-Open No. 77551-1982, Japanese Patent Laid-Open No. 58-77-75)
No. 52, JP-A-58-77554, JP-A-Sho. 5
8-83° 152, etc.), relatively good results have been reported, but the composition-adjusted corrosion-resistant reinforcing bars proposed so far require the addition of expensive special elements, or have insufficient corrosion resistance. However, there remains a need for the development of a reinforcing bar that is less expensive and has sufficient corrosion resistance even in concrete containing chlorides and the like.

From the above-mentioned viewpoint, the present inventors have demonstrated excellent surface corrosion resistance even in concrete containing chlorides, etc.
In order to provide concrete reinforcing bars that can dramatically extend the lifespan of concrete structures in chloride environments at a low cost, first of all, in an alkaline environment in concrete, unlike fully corroding reinforcing bars like in a neutral environment, Pitting type corrosion is a problem, and the effect of alloying elements on the corrosion resistance of reinforcing bars is therefore different from that of steel in the general environment. After doing some basic research on the phenomenon, we found that (a) Pitting corrosion of steel that occurs in an alkaline environment is caused by sulfide-based inclusions (especially Mn5) in the steel that tend to become corrosion starting points. Therefore, suppressing the S content is indispensable to prevent corrosion of reinforcing bars in concrete. When a predetermined amount of Cu is added to the concrete, the pitting corrosion properties of copper are further improved, and it exhibits excellent corrosion resistance and corrosion resistance even in a chloride-containing concrete environment.

(C) As mentioned above, steel containing C11 while suppressing the S content has V, P, Zr, Sn,
When one or more of Y, AiN, and T1 are added and allowed to coexist, the corrosion resistance as reinforcing bars for concrete is further improved, and corrosion hardly occurs in concrete containing chlorides, making it possible to improve reinforced concrete. We have come to the knowledge shown in (a) to (c) above that a remarkable effect is obtained in extending the life of the structure, and the durability and safety are further ensured.

This invention was made based on the above knowledge, and the reinforcing bars for concrete are: C: 0.001 to 0.300% (hereinafter, "C" representing the component ratio is based on weight).

Si: 1.0% or less.

Mn:1. 'I' below.

S: Contains 0.0001 to 0.0100%,
Furthermore, if necessary, it also contains Cu: 0.03 to 0.60%, and V: 0.02 to 0.50%.

P: more than 0.05% and less than 0.15%.

Zr: 0.02-0.80%.

Sn: 0.02-0.60%.

Y: 0.0 1-030%.

At: O, 02-1.00.

N: O, O'L~o, o 5 qb *'I'i
: 0.02~0.30%.

Also includes one or more of the following: Fe and other impurities: Remaining.

It is characterized by significantly improved corrosion resistance, especially against chlorides, by having a component composition consisting of the following.

Next, the reason why the content ratio of the components in the reinforcing bar for concrete of the present invention is numerically limited as described above will be explained.

a) C C is a harmful element that promotes corrosion of reinforcing bars due to chloride, and in particular, if it is contained in excess of 0.30%, a large amount of Fe
Since the corrosion resistance rapidly deteriorates due to the precipitation of 5C, the upper limit of the C content was set at 0.30%.

On the other hand, since reducing the C content i+1 to less than 0.001% exceeds the limit of economical steel production, the lower limit of the C content is set at 0.001%.

b) The 5i S1 component is an element useful as a deoxidizing agent for steel, and the Si content was determined to be 0.5 - 0.

C) Mn Mn is an element that is generally valued for ensuring the strength of steel, but along with S, Mn tends to be the starting point for corrosion.
Since S nonmetallic inclusions are formed, it is desirable to reduce S as much as possible in the reinforcing bars of the present invention. In particular, its content is 1. '7
If it exceeds fi, the corrosion resistance tends to deteriorate significantly, so the Mn content is set at 17% or less. d) S S contains sulfide-based inclusions (mainly Mn5) that act as starting points for corrosion in steel. Therefore, in order to suppress the formation of inclusions, it is safe to keep the content as low as possible. In particular, if S exceeds 0.0100%, H
[Since it was not possible to secure the desired i1 edibility, the upper limit of the S content was set at 0.010'01, on the other hand) -:
Reducing the O, OOO content to less than 1% will result in a significant deterioration of steel manufacturing efficiency and manufacturing costs, so in consideration of economic efficiency, the lower limit of S content 1 is set to 0.0001%.
And so.

e) The cυ Cu component has an excellent effect on improving copper's 1m/1 corrosion resistance, especially pitting corrosion resistance, and its effect becomes even more pronounced when it coexists with component (■), so it may be included as necessary. However, if the content is less than 0.03%, the effect of improving corrosion resistance is not sufficient, and on the other hand, even if the content exceeds 0.50%, it will not dissolve in the steel, so Cu-containing I1
1 was set at 0.03 to 0.60%.

f) v, p, Zr, S++, y, Ag, , N, and Ti These components, in combination with low S, low carbon, low carbon, and C1l addition, improve the quality of the steel] Since it has the same effect as further improving the edibility and providing sufficient performance to withstand even in chloride-containing concrete, one or more of these is added. The reason for limiting the content of the components will be explained in detail below.

■ V The V component has the effect of further improving the feeding ability of low-S steel in an alkaline environment, but when its content is 0
．． If it is less than 0.02%, the desired effect cannot be obtained,
On the other hand, if the content exceeds 0.050%, the hot workability will be adversely affected, so
It was determined that

@ P The P component is a very effective element for improving corrosion resistance, but if its content is less than 0.05%, the desired effect of improving corrosion resistance cannot be obtained, while if it is contained in excess of 0.15%, welding Do not exceed the P content of 0.05%, as this may lead to deterioration of the
．． It was set as 15- or less.

θ Zr The Zr component is an element that contributes to corrosion resistance by forming poorly soluble sulfides, but if its content is less than 0.02%, the desired effect of improving corrosion resistance cannot be obtained; Since Zr content fj4' is set at 0.02 to 0.80%, since Zr content in excess of Zr causes deterioration of weldability like P.

@511 Component 811 exhibits the desired corrosion resistance improvement effect when added in an amount of 0.0% or more, but if it is added in excess of 0.60%, hot workability deteriorates and manufacturing Since ;; 11 contains jJii (
1, (J 2~060chi).

@ Y The Y component is an element that desulfurizes by forming sulfides and thereby improves the corrosion resistance of steel, but if its content is less than 0.01%, the desired effect of improving corrosion resistance cannot be obtained. On the other hand, if the Y content exceeds 0.30%, the weldability deteriorates, so the Y content should be 0.01 to 0.30%.
It was determined that

The AeM component exhibits the desired effect of improving corrosion resistance when added in an amount of 0.02% or more, but if it is added in an amount exceeding 1.00%, weldability deteriorates.
The content was determined to be 0.02 to 1.00%.

■ N The N component is an element that contributes to corrosion resistance by forming ammonium ions when dissolved, but if its content is 0
．． If the N content is less than 0.01%, the desired effect of improving corrosion resistance cannot be obtained, and on the other hand, even if the N content exceeds 0.05%, it will not be completely dissolved in the steel.
It was determined that

■ Tl The T1 component is an element that fixes and stabilizes S by forming hardly soluble sulfides, thereby preventing the formation of MnS, which is the starting point of corrosion. However, if its content is less than 0.02% In this case, the effect of preventing the formation of MnS and obtaining the desired corrosion resistance cannot be sufficiently obtained, and on the other hand, if the content exceeds 0.030 mm, weldability deteriorates, so the T1 content is set to 0.02 ~
0: Decided to be a no-go.

In addition to the above ingredients, 0.005 to 0.0!50
Nb of Chi, and lf of B of O, OOU 3 to O, OO50%! I! Or, if two types are included, the strength can be improved without adversely affecting the corrosion resistance, so this is a preferable means when higher strength is required.

Furthermore, when using the reinforcing bars for concrete according to the present invention, it goes without saying that if +111 lead plating or aluminum plating is applied, the durability of the concrete structure will be further improved.

The reinforcing bars for concrete according to the present invention can be sufficiently manufactured by ordinary melting, casting, and rolling processes, including out-of-furnace refining.

Next, the present invention will be explained in more detail through Examples and in comparison with Comparative Examples.

Example: First, 500 kg of steel having the composition shown in Table 1 was melted in a laboratory using a conventional method including out-of-furnace refining, and hot-rolled in a conventional manner to form a reinforcing bar with a diameter of 20M. 1 to 20 were manufactured.

Next, for each reinforcing bar obtained in this way, the following two
Corrosion tests were conducted under two conditions and the corrosion status was investigated.

○ Test conditions A Width from the center of each reinforcing bar with the composition shown in Table 1: 1
A test piece of 0 mm, length: 50 myn, and thickness of 13 was cut out, polished with No. 320 emery and degreased in sequence, and then added with NaC4 to a saturated Ca(OH)2 aqueous solution adjusted to pH 12. The sample was immersed for 30 days in a test solution containing 0.5% additive at a temperature of 50°C.

○ Test conditions B Length: 03%N
Embedded in concrete (consisting of sand, portland cement, gravel, and water) containing aC1 and exposed outdoors in a coastal area for 6 months. In addition.

The water/cement ratio of the concrete used at this time was 06
And the capri thickness is 10Wu! It was L.

The obtained corrosion test results are also shown in Table 1. In addition, the corrosion status was evaluated by breaking the concrete after the test for test condition A, and by dismantling the concrete and removing the reinforcing bars after the test for test condition B, and evaluating the area ratio of rust occurrence and the maximum hole. The eating depth was measured.

The results shown in Table 1 also show that the reinforcing bars of the present invention have much better corrosion resistance than comparative reinforcing bars that have been used conventionally. In particular, when comparing the maximum depth of pitting corrosion, it was found that the reinforcing bars of the present invention reach only about 1/2 to 1/3 of the depth of the comparative reinforcing bars, demonstrating extremely excellent resistance to corrosion caused by chlorides. It is clear that it has.

As described above, according to the present invention, it is possible to obtain reinforcing bars that exhibit extremely excellent corrosion resistance even in concrete containing chlorides, etc., at a relatively low cost. This brings about industrially useful effects, such as making it possible to sufficiently improve the durability of concrete structures that are forced to live in chloride environments without having to take any countermeasures.

Applicant: Sumitomo Metal Industries, Ltd. Agent Tomi 1) Kazuo and 1 other person

Claims (2)

[Claims] (1) C: 0.001 to 0.3.00% by weight. Sj:i, 0% or less. Mn: 1.7% or more -1. S: Contains U, 0001 to 0.0100%, and ■: 00 to 0.50%. P: More than 0.05% and less than 0.15%. Zr: 0.02~080chi. 811: 0.02-060%. Y: 0.01-030%. AU: 0.02-1.00%. N: rJ, 01-005%. Also includes one or more of Ti: 0.02 to 0.30%, Fe and other unavoidable impurities: the remainder. Reinforcing bars for concrete with excellent corrosion resistance against chlorides, characterized by consisting of: (2) M content ratio: C: 0.001 to 0.300%. Si:1. O Chili bottom. Mn: 1.7- or less. S: O,0OO1-0.0100%. Cu: 0.03-0.60%. Contains V: 0.02 to 0.50%. P: more than 0.05% and less than 0.15%. Zr: 0.02-0.80%. Sn: 0.02-0.60%. Y:0.01~030chi. AQ: 0.02-1.00%. N: 0.01-0.05%. Ti: 0.02-0.30%. Contains one or more of the following: Fe and other unavoidable impurities: Remains. A reinforcing bar for concrete with excellent corrosion resistance against pentachlorides, characterized by comprising: