JPS6254857B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) This invention maintains the durability of concrete that is exposed to salt damage, such as concrete structures using sea sand, concrete for bridges in beach areas, concrete for buildings in beach areas, and concrete for marine structures. This dramatically improves the corrosion resistance of the reinforcing bars themselves. (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. Reinforcing bars with coexistence of Cu and W (Tokukosho)
55-225546, Japanese Patent Application Publication No. 59-44457), 3.5
%Ni added (Japanese Unexamined Patent Publication No. 57-48054)
and so on. Approx. 2 as other salt-resistant reinforcing bars
%Cr has been published (Collection of abstracts of academic lectures at the Architectural Institute of Japan conference, p. 223-224, September 1981). (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. Significantly superior salt tolerance is required even when accumulated salts reach fairly high concentrations. Specifically, it is calculated as 1.2% to 3.6% in aqueous solution.
There is a growing demand for the development of salt-resistant reinforcing bars that exhibit minimal or no rusting at salt concentrations with the highest corrosion rate of 0.3% to 1.0% NaCl (converted to the content in sand in concrete). In order to meet the above-mentioned demands, the present invention aims to dramatically improve the salt resistance of reinforcing bars buried in concrete even in areas with particularly high salt concentrations. This essentially improves the above problems. (Means for Solving the Problems) The concrete reinforcing bars of the present invention have particularly excellent corrosion resistance in a typical concrete corrosive environment where salt is present in the high pH range of concrete,
It is a reinforcing bar that has the necessary mechanical properties and economic efficiency depending on the application, and contains C: 0.05~1.0%, Si: 0.001~
0.05%, Mn; 0.01~2.0%, P; 0.001~0.025
%, S; 0.005% or less, Ni; 1.0 to 5.5%, W; 0.2
Ultra-1.0%, Al: 0.001-0.1%, Ca, Ce, La, singly or in combination, 0.0001-0.1%, with the balance consisting of iron and inevitable impurities,
This is followed by mechanical properties such as high tensile strength,
Considering low-temperature toughness, Nb and V are added to improve weather resistance up to concrete pouring.
Added Cu. The present invention is based on the outstanding salt resistance of concrete reinforcing bars made of high-purity steel with 3.5% Ni added, and the Cu-W system after repeated drying and wetting of concrete blocks containing high concentrations of salt over a long period of time. Focusing on both the superior corrosion resistance of high-purity steel reinforcing bars, and especially
As a result of investigating whether adding W to Ni-based high-purity steel could dramatically improve salt resistance in concrete containing a high concentration of salt, a synergistic effect greater than expected was obtained. Highly purified steel as in the present invention, that is, Si,
When Ni and W coexist in steel with reduced S content, they stabilize the passive film that exists on the reinforcing steel surface in contact with concrete, and at the same time, the steel The W contained therein has the effect of converting very smoothly into a typical inhibitor of WO ₄ ^-- ion, which has a corrosion inhibiting effect. Therefore, the features of the present invention are to lower the Si and S content in the steel so as to stabilize FeO in the P-type semiconductor film, and to add Ni, which produces a typical P-type semiconductor, to increase FeO.
Fe ⁺⁺ is partially replaced with Ni ⁺⁺ to strengthen it, and this reinforced and stable passive film is used to strengthen W in steel.
WO ₄ ^--Easily converted and accumulated into ions. 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 if it exceeds 1.0%, it becomes brittle, so the upper limit was set at 1.0%. Furthermore, the lower limit is set to 0.05% or more because a minimum necessary strength is required. Si tends 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 is difficult to reduce it to an extreme for inclusion control, etc. Can not. Therefore, the lower limit was set to 0.001% and the upper limit was set to 0.05%. Mn is generally known to contribute to increasing the strength of steel. Adding more than 2.0% causes embrittlement, and adding less than 0.01% does not guarantee the strength of a mild steel wire. Therefore, the lower limit of the Mn content was set to 0.01%, and the upper limit was set to 2.0%. 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, it is not possible to reduce the amount of P to an extremely low level. Therefore, the lower limit is 0.001% and the upper limit is
It was set at 0.025%. Since S causes destruction of the passive film due to salt in concrete, it is desirable to reduce it as much as possible. If the content exceeds 0.005%, the passive film will be destroyed and rust will occur, so the content was set at 0.005% or less. The most preferred range is 0.0005-0.002%. Ni is an important element that holds the key to the present invention. It reduces the destruction of the passive film due to salt in concrete as much as possible, stabilizes and strengthens the passive film itself, and at the same time, it strengthens the surface of the (Fe, Ni)O film. It is a very unique element in that it can absorb a large amount of dissolved oxygen, delaying the formation of rust, and at the same time, even if it turns into rust, it can avoid the formation of adhesive rust, which successively promotes the formation of rust. . This effect is
If the amount is less than 1.0%, it cannot be expected, and if it exceeds 5.5%, it is disadvantageous for economic reasons. Therefore, the lower limit is 1.0
%, with an upper limit of 5.5%. W is also an important element in the present invention. Recent research has confirmed that when W is added to high-purity steel, more _WO4 ^-- ions, which are effective in suppressing corrosion, are produced and exert an effect when the Si content in the steel is low. When it coexists with WO 4 -- ions, it is stabilized as mentioned above, and W in steel is easily changed by WO ₄ ^-- ions through (Fe, Ni) O of the P-type semiconductor.
Ni) more traps and accumulates on O,
Even when (Fe, Ni)O turns into rust, it migrates to the (Fe,Ni)O directly beneath the rust, maintaining its corrosion inhibiting effect over a long period of time. Therefore, when it coexists with Ni, it is extremely advantageous for reinforced concrete structures that require durability in summer. In this case, it is particularly noticeable when the addition amount exceeds 0.2%, and it becomes economically disadvantageous when the addition amount exceeds 1.0%. Therefore, the lower limit is 0.2%
(However, excluding 0.2) The upper limit was set at 1.0%. Al is essentially unrelated to corrosion resistance, but it was added to adjust the deoxidizing power due to differences in casting methods, and the lower limit is 0.001 considering the rimmed steel base.
%, and the upper limit was set at 0.1% in consideration of the fact that a large amount of Al is added in continuous cast materials. The main aim of adding Ca, Ce, and La individually or in combination is to significantly reduce the amount of S by desulfurizing the steel, but at the same time, even when the amount of Mn is high, the remaining sulfide becomes complete αMnS. avoid,
It was added in the hope that it would change into a sulfide containing Ca or Ce, change its chemical properties, and improve salt resistance. The lower limit is the minimum necessary content, and is set in the range of 0.0001 to 0.1% to significantly change the properties of the upper sulfide. The addition of Nb and V was aimed at developing salt-resistant reinforcing bars with improved high tensile strength and low-temperature toughness.
V is added singly or in combination to take advantage of the precipitation hardening and fine grain effect of these carbonitrides, and the lower limit was set at 0.005% because the effect is not observed below this. The reason why it is set at 0.2% is that if it exceeds this value, the steel will become brittle. Therefore, each should be in the range of 0.01 to 0.2%. Also, Cu,
is known as an element that improves weather resistance, and particularly contributes to improving corrosion resistance when reinforcing bars are left in the atmosphere before being buried in concrete. 0.01
If the corrosion resistance effect is less than 0.5%, no corrosion resistance effect will be observed.
If it exceeds %, it tends to lead to embrittlement of the steel. Therefore, the lower limit was set to 0.01% and the upper limit was set to 0.5%. According to the present invention, 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 after continuous casting and rolling, if necessary, it is subjected to patenlining. It is subjected to heat treatments such as, etc., and then drawn into wire and used as reinforcing bars. (Example) Example 1 Steel having the composition range of the present invention was melted in a converter, and ingots were formed.
After blooming, the composition and corrosion test results of the drawn reinforcing bars and the reinforcing bars made of conventional steel are shown in the table below. Width 25mm x length 60mm x from the center of each type of reinforcing bar in the table
A specimen with a thickness of 2 mm was taken, and the surface was polished by mechanical grinding. On the other hand, CaO, which is the main component of concrete, is 1.6%.
NaCl, dissolved in 3.6% NaCl aqueous solution to a pH of 12
A Ca(OH) ₂ +NaCl aqueous solution was prepared. 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, dried, and immediately immersed in the above Ca(OH) ₂ +NaCl 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. (A) in the table shows the area where rust occurs (%), and (B) in the table shows the maximum corrosion depth (mm). For reference, some of these specimens have the Ca of PH12 mentioned above.
We investigated the anodic polarization characteristics in (OH) ₂ +16% NaCl aqueous solution. The results are shown in a drawing. It can be seen from the drawings and the table that the potential of the specimens with no rust formation was significantly higher than that of the specimens with rust formation. This is as high as concrete
The passive film on the reinforcing steel that forms in the liquid in the pH range
It has been proven that it is difficult to be destroyed even at high NaCl concentrations of 1.6%. Example 2 Hot-rolled reinforcing bars (9 mmφ) made of the ingredients shown in the table were embedded in concrete mortar made of sand, portland cement, water, and gravel with a NaCl content of 0.5%28
After curing at room temperature for several days, it was exposed to a seashore area for one year. The concrete water/cement ratio was 0.60, and the fog thickness was 2 cm. After one year of exposure, the concrete was destroyed and the rusting status of the reinforcing bars was investigated.The results are shown in table (C). (Effects of the Invention) The present invention is useful as a reinforcing bar for concrete that is extremely effective in maintaining the durability of concrete using sea sand and concrete structures exposed to salt damage, which will become increasingly problematic in the future. The drawing shows Ca(OH) ₂ + 1.6% NaCl aqueous solution (PH
12) shows the positive polarization curve of the test steel measured at 25°C. In addition, the number in the diagram (No.)
indicates the steel number in the table.

【table】

【table】 [Brief explanation of the drawing]

The drawing is a positive polarization curve diagram of the sample steel.

Claims (1)

[Claims] 1 C; 0.05-1.0%, Si; 0.001-0.05%, Mn;
0.01~2.0%, P; 0.001~0.025%, S; 0.005%
Below, Ni; 1.0 to 5.5%, W; more than 0.2 to 1.0%, Al;
0.001~0.1% and Ca, Ce, La alone or in combination
Concrete reinforcing steel with excellent salt resistance, containing 0.0001 to 0.1%, with the remainder consisting of iron and unavoidable impurities. 2C; 0.05-1.0%, Si; 0.001-0.05%, Mn;
0.01~2.0%, P; 0.001~0.025%, S; 0.005%
Below, Ni; 1.0 to 5.5%, W; more than 0.2 to 1.0%, Al;
0.001~1.0% and Ca, Ce, La alone or in combination
Concrete reinforcing steel with excellent salt resistance, containing 0.0001~0.1% Cu, and 0.01~0.5% Cu, with the balance being iron and unavoidable impurities. 3C; 0.05-1.0%, Si; 0.001-0.05%, Mn;
0.01~2.0%, P; 0.001~0.025%, S; 0.005%
Below, Ni; 1.0 to 5.5%, W; more than 0.2 to 1.0%, Al;
0.001~1.0% and Ca, Ce, La alone or in combination
A concrete reinforcing bar with excellent salt resistance, containing 0.0001 to 0.1%, and further containing 0.01 to 0.2% of one or both of Nb and V, with the balance being iron and inevitable impurities. 4 C; 0.05-1.0%, Si; 0.001-0.05%, Mn;
0.01~2.0%, P; 0.001~0.025%, S; 0.005%
Below, Ni; 1.0 to 5.5%, W; more than 0.2 to 1.0%, Al;
0.001~0.1% and Ca, Ce, La alone or in combination
Contains 0.0001~0.1% and further Cu0.01~0.5%
Concrete reinforcing bars with excellent salt resistance, containing 0.01 to 0.2% of each of Nb and V, with the remainder being iron and unavoidable impurities.