JPS61143559A - Reinforcing rod for concrete having superior salt resistance - Google Patents

Abstract

PURPOSE:To obtain a reinforcing rod for concrete having superior salt resistance by incorporating Ni and W into a steel having reduced Si and S contents. CONSTITUTION:The composition of a reinforcing rod for concrete is composed of, by weight, 0.001-1% C, 0.001-0.05% Si, 0.01-2% Mn, 0.001-0.025% P, <0.005% S, 1-5.5% Ni, 0.2-1% W, 0.001-0.1% Al, 0.0001-0.1% Ca and/or Ce and the balance Fe with inevitable impurities. The composition may furthecontain one or more among 0.01-0.2% each of Nb, Ti, V and Mo and 0.01-0.5% each of Cu and Cr.

Description

[Detailed Description of the Invention] (Field of Industrial Application) This invention is applicable to concrete structures using sea sand, concrete for bridges in coastal areas, concrete for buildings in sand fishing areas, concrete for marine structures, etc. that are exposed to salt damage. In order to maintain the durability of concrete, the corrosion resistance of the embedded reinforcing bars themselves has been dramatically improved.

(Prior art) There are various methods to maintain the durability of concrete exposed to salt damage, but the inventors of this application have developed a method that improves the salt resistance of the reinforcing bars themselves. C
U, W coexisting reinforcing bars (Special Publication No. 55-22546,!#
(Japanese Patent Application Laid-open No. 57-48054) and 3.5% N1t-added (Japanese Patent Application Laid-Open No. 57-48054). Other salt-resistant reinforcing bars containing approximately 24Cr have been published (Collection of Abstracts of Academic Lectures at the Architectural Institute of Japan, p. 22)
3-224, September 1983).

(Problems to be Solved by the Invention) It has become possible to manufacture concrete structures with high resistance to salt damage using the above-mentioned reinforcing bars for concrete, which the inventors of the present application have already announced. Remarkably excellent salt tolerance is required even if the salt accumulated in the water reaches a very high concentration. Specifically, the content is 1.2 to 3.6% NaCJ in aqueous solution, and 0.3 to 1% in terms of content in sand in concrete. O% There is a growing demand for the development of salt-resistant reinforcing bars that exhibit minimal or no rusting at the salt concentration where the corrosion rate is highest in NiCJ.

In order to meet the above-mentioned demands, the present invention aims to dramatically improve the salt resistance of reinforcing bars buried in conocret, even in areas with particularly high salt concentrations. This essentially improves the above problems.

(Means for solving the problem) The reinforcing bars for concrete of the present invention have high pH in concrete.
C; 0.0 for reinforcing bars that have particularly excellent corrosion resistance in the typical concrete corrosive environment where salt is present in the area, and have the necessary mechanical properties and economy depending on the application.
01, to%, 5iHQ, 001~0.05%,
Mn; 0.01~ZOTo, P, 0.001
~0.025%, s, o, oos or less, Ni; L
0-5.5%, W; more than 0.2-1. O%, 0.0 to A
The first invention is one containing 0.0001 to 0.1% of Ca%Ce (may be accompanied by La11!), alone or in combination, with the balance consisting of iron and unavoidable impurities. Next, mechanical properties such as high tensile strength,
The second invention is one in which Nb, Ti%V%Nb, etc. are added in consideration of low-temperature toughness, and Cu and Crt- are added in order to improve weather resistance up to concrete pouring.

The present invention is based on the fact that concrete reinforcing bars made of high-purity steel with 3.5-Ni added have excellent salt resistance, and that concrete blocks containing high concentrations of salt can survive repeated drying and wetting at high temperatures for a long period of time. Focusing on both the excellent corrosion resistance of Cu-W based high purity steel reinforcing bars, in particular, by adding wt- to Ni based high purity steel, dramatic salt resistance can be obtained in concrete containing a high concentration of salt. As a result of considering whether or not it was possible, we found that the synergistic effect was greater than expected.

When Nt and W are made to coexist in highly purified steel as in the present invention, that is, steel with reduced Sl and S, it stabilizes the passive film existing on the reinforcing steel surface in contact with concrete, and at the same time of the coating (Fe.

N1) Through the Pfi semiconductor of O, W in steel has a very smooth corrosion inhibiting effect, and has the effect of changing the typical inhibitor of -io/. Therefore, the feature of the present invention is to lower the 81, S in the steel to stabilize the F@0 of the P-type semiconductor film, and to reduce the N1 to produce a typical P-type semiconductor.
The steel is strengthened by adding T- to partially replace Fe0Fe with Ni, and by utilizing this strengthened and stable passive gXt, the conversion and accumulation of W in the steel to WO4- ions is facilitated.

In order to achieve this effect, the component range of the reinforcing bar of the present invention was determined as follows. Let me explain the reason.

C is essential for increasing mechanical strength, but 1. The upper limit was set at 1.0 inch because it becomes brittle if the temperature is too high. Also, the lower limit is O, 0
The reason why it is set at 01% is because a soft, small diameter steel wire is required for the mild steel wire when connecting reinforcing bars.

Sl has a tendency to deteriorate the passive film on the surface of reinforcing bars embedded in concrete, so it is desirable to reduce it as much as possible, but its presence in steelmaking is unavoidable, and it cannot be reduced to an extreme degree from the perspective of controlling inclusions. Can not. Therefore, the lower limit 'io, oo was set as 1%, and the upper limit was set as t-o, oschi.

Calmness is generally known to contribute to increasing the strength of steel. If added in excess of λOs, it will become brittle and 90,0.01n
If it is less than that, the strength as a mild steel wire cannot be guaranteed. Therefore, the lower limit of stopping was set as t-o, ois, and the upper limit was set as t-10.

P is generally known as an element that improves seawater resistance, but in concrete, reducing the amount of P contributes to improving salt resistance. However, for steel manufacturing reasons, P
It is not possible to reduce the amount of Therefore, the lower limit t
-0,0011, and the upper limit was set to 0.025 inches.

It is desirable to reduce S as much as possible since it causes wave breakage of the passive '4i film due to salt in the concrete. o
If the content exceeds o, oos, the passive film will be destroyed and rust will occur, so the content is set to be less than o, oos*. The most preferred range is o,oos to 0.002%.

Ni is an important element that holds the key to the present invention. It reduces the possibility of destruction of the passive film due to salt in concrete, stabilizes and strengthens the passive film itself, and at the same time stabilizes and strengthens the passive film itself.
%Ni) O adsorbs a large amount of dissolved oxygen on the surface of the coating, delaying the formation of rust, and at the same time avoiding the formation of adhesive rust that successively promotes the formation of rust even if it changes to rust. It is an extremely distinctive element. This effect cannot be expected when the Ni content is less than 1.0, and it becomes disadvantageous for economic reasons when the Ni content exceeds S or SS. Therefore, its lower limit t-
LO9g, upper limit 5.5%.

W is also an important element in the present invention. Recent research has confirmed that when Wt- is added to high-purity steel, if the amount of added W is low in the steel, more WO4''''- ions, which are effective in inhibiting corrosion, are generated and are effective. When it coexists with Ni, it is stabilized as mentioned above and the (Fe
, Ni) Of, W in the steel easily changes into WO4-'''' ions, and more of it is trapped and accumulated on (F4!, N1)0, causing (Fe, N1)0 to change into rust. However, the corrosion suppressing effect is maintained over a long period of time by transferring to the (Fe, Ni 10) directly under the rust.

Therefore, when it coexists with Ni, it is extremely advantageous for reinforced concrete structures that require fire resistance in summer. In this case, it is especially noticeable when the amount added exceeds 0.2 inch.
Exceeding - will put you at an economic disadvantage.

Therefore, the lower limit t-0.2ch (but does not include 0.2)
The upper limit was set as fcLO%.

M is essentially unrelated to corrosion resistance, or is added to adjust the deoxidizing power due to differences in casting methods.The lower limit is O,001% considering the rimmed steel pace, and the upper limit is for continuous casting. Considering that a large amount of M is added to materials, etc., it was set to 0.1 inch.

The main aim of adding CζCo (Lm is often performed) alone or in combination is to significantly reduce the amount of brittle sulfur (S) in steel, but at the same time, even when the amount is high, residual sulfide It was added in the hope that it would avoid turning into a complete αMnS, change it into a sulfide containing Ca or Ce, change its chemical properties, and improve its salt resistance.

The lower limit is the minimum necessary content, and the upper limit is 0.000, which is specified to significantly change the properties of the sulfide.
The range was 1 to 0.11.

Note that Co is not accompanied by Lat, and is effective even if it includes -.

For the second invention, the addition of v,'rt%an is aimed at developing salt-resistant reinforcing bars with improved high tensile strength and low-temperature toughness.
Tooth, 7% Ti, and Mu are added singly or in combination to take advantage of the extraction hardening and fine grain effect of these carbonitrides, and the lower limit t-o, oos* was set because below this, the effect is recognized. The reason why the upper limit was set at 0.2 inch is that if it exceeds this value, the steel will become brittle. Therefore, each range is set to 0.01 to 0.2 inches. Further, Cu and Cr of the second invention are known as elements that improve weather resistance, and particularly contribute to improving corrosion resistance when reinforcing bars are left in the atmosphere before being buried in concrete. If it is less than 0.01 inch, no corrosion resistance effect will be observed, if it exceeds 0.5 inch in the case of Cu, it will lead to embrittlement of the steel, and if it exceeds 0.5 inch in the case of Cr, pitting corrosion due to salt will easily occur in concrete. Therefore, the lower limit was set to t-0.01%, and the upper limit was set to O.S.

According to the present invention, the steel composed of the above chemical components is melted in a converter, electric furnace, etc., and then passes through the steps of ingot making and blooming, or
Alternatively, after continuous casting and rolling, heat treatment such as snaplining is performed as necessary, and wire is drawn to serve as reinforcing bars. Further, the surface can be galvanized or coated with an organic layer if necessary.

(Example) Example 1 Steel having the composition range of the present invention was melted in a converter, and after ingot formation and blooming,
The table below shows the composition and corrosion test results of the drawn reinforcing bars and the reinforcing bars made of conventional steel.

Samples measuring 25 mm in width x 60 mm in length x 2 mm in thickness were taken from the medium-heated parts of various reinforcing bars on the table, and the surfaces were polished by mechanical grinding.

On the other hand, CaOfCl, which is the main component of concrete, 6
%NaC7,3,6*Na(J aqueous solution was dissolved to pH 1: OCa(OH), +Na(J aqueous solution).

Thereafter, the surface of the sample was ground as described above, the side and back surfaces were coated with silicone resin, and the sample was degreased and dried, and immediately immersed in the above Ca (OH), + NaCJ3 aqueous solution. During the test, the surface of the liquid was sealed with liquid paraffin, and the liquid was replaced every 3 days, and the samples were immersed continuously for 20 days to observe the occurrence of rust.

In the table (Al indicates the area where rust occurs (ch), and (B) in the table indicates the maximum corrosion depth.
The anodic polarization characteristics were investigated in a 1.6% NaCJ aqueous solution.

The results are shown in a drawing.

It can be seen from the drawings that the stains are significantly more to blame for the items for which no rust was observed than for the items for which rust was observed. This proves that the passive coating of reinforcing bars, which is formed in liquids in a high pH range such as concrete, is difficult to be destroyed even when the NaCJ concentration is as high as 1.6%.

Example 2 Hot-rolled reinforcing bars (9 silk φ) from the ingredients shown in the table were embedded in a concrete mortar consisting of sand, portland cement, water, and gravel with an NaCJ content of 0.5%, and after curing at room temperature for 28 days, it was placed on a beach. exposed to the zone for one year. The water/cement ratio of concrete was 0.60° and the capri thickness was 20.

After one year of exposure, the concrete is destroyed and the reinforcing bars are rusted f
: The results are shown in (C) of the table.

(Effects of the Invention) The present invention is useful as an extremely effective reinforcing bar for concrete in order to maintain the durability of concrete using sea sand and concrete structures exposed to salt damage, which will become increasingly problematic in the future.

In the drawing, Ca (OH)t + 1.61 NJLC
J7) It shows the anodic polarization curve of the test steel measured at 25° C. in a C solution (pH 12). Note that the number (A) in the figure indicates the steel layer on the front.

- Rono

[Brief explanation of drawings]

The drawing is a positive polarization curve diagram of the sample steel. Patent Applicant: Nippon Steel Corporation = %A (x'¥y, 5s, ., 6) Procedures Amendment V (voluntary) May 9, 1925 Manabu Shiga, Commissioner of the Patent Office 1, of the case Description: Japanese Patent Application No. 59-265277 2, Title of the invention: Concrete reinforcing steel bar with salt resistance 3, Relationship to the amended case: Applicant (665) Nippon Steel Corporation 4, Agent: Toranomon, Minato-ku, Tokyo -Chome 1-18-5, Subject of amendment Detailed description of the invention in the specification. 6. Contents of the amendment (1) Page 2 of the specification, lines 4 to 6, it says, "Concrete structures, concrete for construction in beach areas," and "Concrete structures, REITs in beach areas." and correct it. (2) On page 3, line 9 of the specification, amend "in rNaCL" to "in rNaCL." (3) On page 4 of the specification, line 1, r Nb, Ti,
V, Nb J, rNb, Ti, V, MOJ
and correct it. (4) On page 5, line 9 of the specification, the phrase "action to change the inhibitor" should be corrected to "action to change to the inhibitor." (5) Page 6 lines 9-10 of the specification, “Embrittled C,
It says "J", but I corrected it to "become brittle." (6) On page 9, line 7 of the specification, it says, "Ce is never accompanied by L&," which has been amended to read, "In addition, (, l is often accompanied by L&.") (7) Specification Book page 9, line 11, r Nb, V, Ti, Mn
J is corrected to r Nb, V, Tl, Mo J. that's all

Claims (2)

[Claims] (1) C: 0.001~1.0%, Si: 0.001~
0.05%, Mn; 0.01-20%, P; 0.001
~0.025%, S; 0.005% or less, Ni; 1.0
~5.5%, W; more than 0.2 ~ 1.0%, Al; 0.00
1 to 0.1%, and Ca and Ce alone or in combination to 0.
A concrete reinforcing bar with excellent salt resistance containing 0001 to 0.1% with the balance being iron and unavoidable impurities. (2) C: 0.001~1.0%, Si: 0.001~
0.05%, Mn; 0.01-2.0%, P: 0.00
1 to 0.025%, S; 0.005% or less, Ni; 1.
0 to 5.5%, W; more than 0.2 to 1.0%, Al; 0.0
01 to 0.1%, and Ca and Ce alone or in combination.
．． 0001 to 0.1%, and further contains Nb as necessary.
, Ti, V, Mo, Cu, Cr alone or in combination with N
b, Ti, V, Mo are each 0.01 to 0.2%, Cu,
Concrete reinforcing bars with excellent salt resistance, each containing 0.01 to 0.5% of Cr, with the remainder consisting of iron and impurities.