JPS645099B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to improving the corrosion resistance of reinforcing bars for concrete, and in particular to reducing local corrosion of reinforcing bars due to salt in sea sand, which has become a concern with the recent increase in the use of sea sand. The aim is to develop reinforcing bars used in architectural concrete, etc. In general, concrete has a pH value of approximately 12.5 at the time of pouring.
Generally, the pH value of concrete that passes the usage standards for architectural concrete exposed to the atmosphere is around 12. At such a high pH value, in the absence of salt, the surface of the reinforcing steel in concrete is covered with a passive film and corrosion does not progress. However, even if the PH value is high, if salt is present in the concrete around the reinforcing bars, the salt will destroy a part of the passive film, and corrosion of the steel will progress significantly in that area, causing local corrosion. provoke. Therefore, with the use of salt-containing sand such as sea sand as a raw material for concrete, the problem of local corrosion of concrete reinforcing bars due to salt has recently become more and more common, even though corrosion has rarely been a problem in the past. It has been. The present invention responds to changes in these social circumstances,
The purpose of this product is to significantly improve the salt resistance of concrete reinforcing bars.The feature is that the reinforcing bars themselves have corrosion resistance, and in particular, by reducing pitting corrosion and local corrosion, the above problems can be essentially solved. This is an improvement. Furthermore, it is used with a galvanized coating if necessary, and has excellent corrosion resistance in the corrosive environment where salt is present in the high PH range of concrete mentioned above, and has the necessary mechanical properties and properties depending on the application. Regarding economical reinforcing bars, C:
0.001~1.0%, Si: 0.005~0.05%, Mn: 0.01~
1.2%, P: 0.005-0.05%, S: 0.0005-0.003%,
Contains Al: 0.001-0.08%, Ca: 0.0002-0.001%,
The first invention relates to reinforcing bars that are composed of residual iron and unavoidable impurities and that have excellent corrosion resistance when salt from sea sand is present in concrete with a pH of around 12. Considering mechanical properties such as low temperature toughness, Nb , V, Ti, and Ni added to the second and third
In addition, the second invention is one in which Cu is appropriately added to ensure weather resistance until it is poured into concrete. Conventionally, the salt resistance of concrete reinforcing bars was improved by adding elements to the steel.
No. 55-22546, the main technical idea of which is to prevent pitting corrosion by adding tungsten salt and generating tungsten salt in concrete. In response to this, the present invention adds Ca to the current ordinary reinforcing bars to significantly reduce the S content in the steel, and at the same time reduces the amount of Si in the steel as much as possible to create a coating on the surface of the reinforcing bars. By changing the chemical properties of sulfide, which causes salt film damage, to a more salt-resistant one, and at the same time significantly reducing the amount of Si compounds present in the film, we are creating a non-sulfide with excellent salt resistance. Its feature is that it forms a functional film. Therefore, the biggest feature is to reduce the amount of Si and S in the steel as much as possible, and to add a relatively small amount of Ca to change the properties of sulfides.
The aim of the present invention is to focus on cases where salt is present in a high pH range of around 12, such as in concrete. The details will be described below, and the reason why the component ranges of the reinforcing bars of the present invention were determined as described above will be explained. When the upper limit of the Mn content is set at 1.2%, C is essential for increasing mechanical strength, so the upper limit is set at 1.0%. The lower limit was set to 0.001% because a soft, small-diameter steel wire is required for connecting reinforcing bars. 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. Can not. Therefore, the lower limit was set to 0.005% and the upper limit was set to 0.05%. A more preferred range is 0.005
~0.02%. Mn is generally known to be involved in increasing the strength of steel and generating sulfides. As for sulfides, it is desirable that manganese sulfide-based sulfides, which are the starting point for destroying the passive film on the surface of reinforcing bars embedded in concrete, be as small as possible. Therefore Mn
A lower amount is preferable, but in order to ensure the necessary mechanical strength, the lower limit was set to 0.01% and the upper limit was set to 1.2%. P is generally known as an element that improves seawater resistance, but increasing the amount of P deteriorates weldability. Therefore, the lower limit is 0.005% and the upper limit is 0.05%.
And so. As mentioned above, S causes destruction of the passive film due to salt in concrete, so it is desirable to reduce it as much as possible. However, reducing the content to below 0.0005% is economically disadvantageous. Therefore, the lower limit was set to 0.0005% and the upper limit was set to 0.003%. The most preferred range is 0.001-0.002%. Al is not essentially related to corrosion resistance, but it was lowered to adjust the deoxidizing power due to differences in casting methods, and the lower limit is based on rimmed steel.
It was set at 0.001%, and the upper limit was set at 0.08% in consideration of the fact that a large amount of Al is added in continuous casting materials. The main aim of adding Ca is to desulfurize the steel and reduce the S content.
The aim is to significantly reduce the amount of Mn, but at the same time
Even when the amount of residual sulfide is high, the remaining sulfide is completely αMnS.
It was added in hopes of improving salt tolerance by changing its chemical properties by turning it into a sulfide containing Ca. The lower limit is the minimum necessary content, and the upper limit is specified to significantly change the properties of sulfide, and is from 0.0002 to
The range was set at 0.001%. The addition of Nb, V, and Ti in the second invention was aimed at developing high-tensile salt-resistant reinforcing bars, and in order to increase mechanical strength, these carbonitride-forming elements were added for the purpose of precipitation hardening and fine grain effect. It has characteristics. The reason why the lower limit was set at 0.005% is because the effect is not recognized below this, and the reason why the upper limit was set at 0.2% is because above this, the steel becomes brittle. The amount of Cu added was determined in consideration of the need for weather resistance, and the lower limit is the minimum amount necessary to achieve the effect, and the upper limit is the amount that causes embrittlement of the steel, and was set at 0.03 to 0.5%. The addition of Ni in the third aspect of the invention is also aimed at improving the low-temperature toughness when this reinforcing bar is used as a reinforcing bar for concrete in cold regions. Good properties were observed for Ni at 1.0% or more, and at 5.5%
In the above case, the amount of Ni was limited because it would be economically disadvantageous. According to the present invention, the steel composed of the above chemical components is melted in a converter, electric furnace, open hearth, etc., and then ingot-formed,
After completing the blooming process or after being continuously cast and rolled, it is subjected to heat treatment such as patenting or drawn as required, and then used as reinforcing bars. Additionally, the surface may be galvanized if necessary. Example 1 Table 1 shows the composition and corrosion test results of reinforcing bars made of steel having the composition range of the present invention in a converter, ingot-formed, and bloomed, and drawn, and of conventional steel. Width 25mm x length from the center of the reinforcing bars shown in Table 1
A specimen of 60 mm x 2 mm thickness was taken and mechanically ground to polish the surface. On the other hand, CaO, the main component of concrete, is 0.2%.
Ca(OH) ₂ + at pH 12 dissolved in NaCl aqueous solution
A NaCl aqueous solution was prepared. Thereafter, the surface of the specimen was ground as described above, the measured surface and the back surface were coated with silicone rubber resin, and the specimen was degreased with benzol and acetone, dried, and immediately immersed in the above Ca(OH) ₂ +NaCl aqueous solution. Seal the surface of the liquid with liquid paraffin, and
The liquid was replaced every day and the samples were immersed continuously for 20 days, and the state of rust formation was observed. (A) in the table indicates the presence or absence of rust, and (B) in the table indicates the depth of local corrosion in mm. For reference, the anodic polarization characteristics of some of these specimens were examined in the aforementioned PH12 Ca(OH) ₂ +NaCl aqueous solution. The results are shown in FIG. From FIG. 1, it can be seen that the potential of the specimens in Table 1 in which rust was not detected is higher than that of the specimens in which rust was observed. This proves that the passive film of reinforcing steel, which forms in liquids in high pH ranges such as concrete, is difficult to be destroyed by NaCl. Example 2 Reinforcing bars (9 mmφ) made of the ingredients shown in Table 1 were embedded in a concrete mortar made of sand containing salt containing 0.2% NaCl (%), Portland cement, water, and gravel, and kept at room temperature for 28 days. After curing,
Exposure to beach area for 1 year. The water-to-cement ratio of the concrete was 0.65, and the fog thickness was 2 cm. The reinforcing bars are hot rolled reinforcing bars. After one year of exposure, the concrete was crushed and the rusting status of the reinforcing bars was examined. The results are shown in Table 1 (C).

【table】

【table】 [Brief explanation of the drawing]

Figure 1 shows Ca(OH) ₂ + 0.2% NaCl aqueous solution (PH12)
Among them, the anodic polarization characteristics of the test steel measured at 25°C are shown.

Claims (1)

[Claims] 1 C: 0.001 to 1.0%, Si: 0.005 to 0.05%,
Mn: 0.01-1.2%, P: 0.005-0.025%, S:
0.0005~0.003%, Al: 0.001~0.08%, Ca:
A reinforcing bar for concrete that contains 0.0002 to 0.001%, with the balance consisting of iron and unavoidable impurities, and has excellent corrosion resistance when salt is present in concrete. 2 C: 0.001-1.0%, Si: 0.005-0.05%,
Mn: 0.01-1.2%, P: 0.005-0.025%, S:
0.0005~0.003%, Al: 0.001~0.08%, Ca:
Contains 0.0002 to 0.001% and 0.005 to 0.2% of Nb, V, and Ti either singly or in combination, and further contains Cu of 0.03%.
% to 0.5%, with the balance consisting of iron and unavoidable impurities, and has excellent corrosion resistance when salt is present in concrete. 3 C: 0.001~1.0%, Si: 0.005~0.05%,
Mn: 0.01-1.2%, P: 0.005-0.025%, S:
0.0005~0.003%, Al: 0.001~0.08%, Ca:
A reinforcing bar for concrete that contains 0.0002 to 0.001% and 1.0 to 5.5% Ni, with the balance consisting of iron and unavoidable impurities, and has excellent corrosion resistance when salt is present in concrete.