JPS6311424B2 - - 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 intruding from the marine environment and salt in sand, and is applicable to concrete for bridges in coastal areas, architectural concrete in desert areas, and marine structures. The aim is to develop reinforcing bars for use in concrete, etc. In general, concrete has a PH value of about 12.5 when poured, and although it passes the standards for use in architectural concrete when exposed to the atmosphere, the PH value is generally around 12. At such high PH values, in the absence of salt, the reinforcing steel surface in concrete is passive and easily wetted. 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, inducing local corrosion. . Therefore, as salt-containing sand such as desert sand or sea sand is used as a raw material for concrete, corrosion of concrete reinforcing bars has rarely been considered a problem, but local corrosion of concrete reinforcing bars due to salt has recently become a problem. The problem has been brought into close focus. The purpose of the present invention is to significantly improve the salt resistance of concrete reinforcing bars in response to such circumstances.The feature is that the reinforcing bars themselves have corrosion resistance, and in particular, by reducing pitting corrosion and local corrosion, This essentially improves the problems of . The reinforcing bars for concrete of the present invention are used with a galvanized coating if necessary, and have excellent corrosion resistance in the above-mentioned corrosive environment where salt is present in the high PH range of concrete, and are suitable for use. C: 0.01 to 1.0%, Si: 0.005 to 0.05%, with reinforcing bars that have the necessary mechanical properties and economic efficiency.
Mn: 0.1~2.0%, Cr: 0.05~0.4%, Cu: 0.01~
0.4%, P: 0.005-0.025%, S: 0.003% or less,
The first invention is one containing Al: 0.01 to 0.1%, less than 0.0002 to 0.005% Ca, and the balance is iron and unavoidable impurities.Following this, the next invention is one to which Ni is added in consideration of low temperature toughness. This is considered as the second invention. Furthermore, considering high tensile strength and low temperature toughness, Nb, V,
The third invention is one to which Ti, Mo, and W are added. Conventionally, the salt resistance of concrete reinforcing bars was improved by adding elements to the steel, and the
-22546, the main idea of which is to prevent the occurrence of pitting corrosion by adding tungsten salt and forming tungsten salt in concrete. Next, the inventors, who are the same as those of the present invention, added Ca and Rem singly or in combination to current ordinary reinforcing bars to significantly lower the S content in the steel, and at the same time, developed a high-purity steel in which the amount of Si in the steel was reduced. Cu on high purity steel
It was found that salt resistance was significantly improved by adding elements such as Ni and Ni, and an application was filed as Japanese Patent Application No. 113047-1983 (Japanese Patent Application Laid-open No. 57-48054). The present invention is a further development of the technical idea of the above-mentioned invention, and further improves corrosion resistance. That is, by adding Cu, which is a weather-resistant element, and further adding Cr, which has seawater resistance, in an amount that does not cause pitting corrosion, the salt resistance is significantly improved. 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. 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 was set to 0.05% 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, etc. Can not. Therefore, the lower limit was set to 0.005% 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 0.1% does not guarantee the strength of a mild steel wire. Therefore, the lower limit of the Mn content was set to 0.1%, and the upper limit was set to 2.0%. 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 0.025%.
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. If the content exceeds 0.003%, the passive film will be destroyed and rust will occur.
% or less. The most preferred range is 0.0005~
It is 0.002%. Cu is known as an element that improves weather resistance, and it particularly contributes to improving corrosion resistance when reinforcing bars are left exposed to the atmosphere before being buried in concrete. If it is less than 0.01%, no corrosion resistance effect is observed;
If it exceeds %, it leads to embrittlement of the steel. Therefore, the lower limit of the amount added was set to 0.01% and the upper limit was set to 0.05%. Cu is unavoidably 0.2 when using scrap.
%, but its effectiveness is recognized in this case as well. Cr is known as a seawater resistant element, but 0.5%
If excessively added, pitting corrosion and deterioration due to salt will be significant.
No effect is observed at less than 0.05%. Therefore, the upper limit of the amount added is 0.5%, and the lower limit is 0.5%.
It was set as 0.05%. Adding an appropriate amount of Cr to high-purity steel as described above promotes the strengthening of the passivation film in concrete and reduces deterioration due to salt. Cr is unavoidably 0.1% when using scrap
Although there are cases where the front and back are mixed, effectiveness is recognized in this case as well. Al is essentially unrelated to corrosion resistance, but is added to adjust the deoxidizing power due to differences in casting methods.The lower limit is 0.01%, and the upper limit is the addition of a large amount of Al in continuous casting materials, etc. Considering this, it was set at 0.1%. The main aim of Ca is to significantly reduce the amount of S through desulfurization in steel, but at the same time, even when the amount of Mn is high, the remaining sulfide is prevented from becoming complete αMnS, and changes to sulfide containing Ca. It was added in the hope that it would change its chemical properties and improve its salt tolerance. The lower limit is the minimum necessary content, and the upper limit is defined to significantly change the properties of sulfide, and is in the range of 0.0002 to less than 0.005%. The addition of Ni in the second invention aims to improve the low-temperature toughness especially when used as reinforcing bars for concrete in cold regions, and if it is less than 0.05%, the effect will not be recognized, and if it exceeds 5.5%, it will be economically disadvantageous. The amount of Ni was limited to Furthermore, the addition of Nb, V, Ti, Mo, and W in the third invention was aimed at developing salt-resistant reinforcing bars with the aim of improving high tensile strength and low-temperature toughness.
The addition of carbonitrides takes advantage of the precipitation hardening and fine grain effect of these carbonitrides.The lower limit was set at 0.01% because the effect was not observed below this, and the upper limit was set at 0.2%. This is because if it exceeds this, the steel becomes brittle. 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 passing through the blooming process or after continuous casting and rolling, the steel is subjected to heat treatment such as patenting as necessary, and drawn into wire to be used as reinforcing bars.
Further, the surface may be galvanized or coated with an organic coating, if necessary. Example 1 of the present invention The table 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, bloomed, and drawn, and reinforcing bars made of conventional steel. Width 25mm x length 60mm from the center of the reinforcing bars shown in the table
× A specimen with a thickness of 2 mm was taken and mechanically ground to polish the surface. On the other hand, CaO, which is the main component of concrete, is 0.8%.
Ca(OH) ₂ + at pH 12 dissolved in NaCl aqueous solution
A NaCl aqueous solution was prepared. Thereafter, the specimen whose surface was ground as described above and whose side and back surfaces were coated with silicone resin was degreased, dried, and immediately immersed in the Ca(OH) ₂ +NaCl aqueous solution described above. During the test, the surface of the liquid was sealed with liquid paraffin, 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 indicates the presence or absence of rust, and (B) in the table indicates the depth of local corrosion in mm. For reference, some of these specimens have the above-mentioned PH12 Ca(OH) ₂ + NaCl
The anodic polarization characteristics were investigated in aqueous solution. The results are shown in the drawing. It can be seen from the drawings and the table that the potential of the specimens with no rust formation is higher than that of the specimens with rust formation. This proves that the passive coating of reinforcing bars, which is formed in liquids in the high pH range such as concrete, is difficult to be destroyed by NaCl. Example 2 of the present invention Hot-rolled reinforcing bars (9 mmφ) made of the ingredients shown in the table in a concrete mortar made of sand containing 0.2% NaCl (%), Boltland cement, water, and gravel
After filling and curing at room temperature for 28 days, it was placed in a seaside area.
Exposure for years. The water-cement ratio of the concrete was 0.65, and the fog thickness was 2 cm. After one year of exposure, the concrete was crushed and the occurrence of reinforcing bars was compared. The results are shown in Table (C).

[Table] The drawing shows the anodic polarization characteristics of the test steel measured in Ca(OH) ₂ + 0.8% NaCl aqueous solution (PH12) at 25°C.

[Brief explanation of the drawing]

The drawings are graphical diagrams.

Claims (1)

[Claims] 1 C: 0.05-1.0%, Si: 0.005-0.05%, Mn:
0.1~2.0%, Cr: 0.05~0.4%, Cu: 0.01~0.4%,
P: 0.005-0.025%, S: 0.003% or less, Al: 0.01
~0.1%, less than 0.0002 to 0.005% Ca, with the balance consisting of iron and unavoidable impurities, and has excellent corrosion resistance when salt is present in concrete. 2 C: 0.05-1.0%, Si: 0.005-0.05%, Mn:
0.1~2.0%, Cr: 0.05~0.4%, Cu: 0.01~0.4%,
P: 0.005-0.025%, S: 0.003% or less, Al: 0.01
~0.1%, less than 0.0002 to 0.005% Ca, and 0.05 to 5.5% Ni, with the remainder being iron and unavoidable impurities, and has excellent corrosion resistance when salt is present in concrete. 3 C: 0.05-1.0%, Si: 0.005-0.05%, Mn:
0.1~2.0%, Cr: 0.05~0.4%, Cu: 0.01~0.4%,
P: 0.005-0.025%, S: 0.003% or less, Al: 0.01
Contains ~0.1%, less than 0.0002~0.005% Ca, and 0.01~0.2% of Nb, Ti, V, Mo, and W alone, with the balance consisting of iron and unavoidable impurities, and salt is present in the concrete. Reinforcing bars for concrete with excellent corrosion resistance.