JPH0480112B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention is applicable to steel structures and concrete structures, particularly those installed in marine environments and coastal areas.
Transportation equipment that is installed in environments where road antifreeze is sprayed, or that travels in these environments,
For example, it relates to steel used in harsh salt environments such as automobiles and vehicles. That is, the purpose of the present invention is to provide a steel suitable for the above-mentioned uses, and since the steel itself has good seawater resistance, it can be used to prevent deterioration of structures installed in oceans and coastal areas. environment such as
This relates to seawater-resistant steel that is useful for preventing deterioration of transportation equipment such as automobiles that run on expressways that are sprayed with road antifreeze agents such as NaCl and CaCl. (Prior Art) Recently, various prevention methods have been proposed and put into practice to prevent deterioration of steel structures and concrete structures installed in oceans and coastal areas.
The biggest cause of deterioration in steel structures is corrosion caused by seawater itself and corrosion by sea salt particles, but the biggest cause of concrete deterioration is corrosion caused by salt penetrating through concrete walls. The reinforced steel corrodes, and its volume is approximately the same as that of steel.
Since the expansion force increases by 2.2 times, the concrete along the buried reinforcing bars can no longer withstand the expansion force and cracks occur. If the crack is 0.2 mm or more, external corrosion factors such as oxygen, salt, and carbon dioxide in the air will more easily penetrate through the crack to the area around the buried reinforcing steel, further promoting corrosion of the steel or damaging the concrete. This will promote carbonation and accelerate the deterioration of concrete. In addition, in winter, on expressways where road antifreeze has been sprayed, the rich salt causes rapid deterioration of not only the roads but also the cars traveling on these roads due to corrosion, and measures are taken to prevent this deterioration. Although various prevention methods have been implemented, it has not yet been possible to completely stop the deterioration. Now, among these, the deterioration of concrete due to salt damage has recently received a lot of attention, so the conventional techniques for preventing this deterioration will be described below. In order to prevent such deterioration of concrete, the present inventors conducted research to improve the salt resistance of the reinforcing bars themselves by controlling the chemical composition of the reinforcing bars themselves, and as a result of their research, they developed reinforcing bars for concrete with significantly improved salt resistance. (Unexamined Japanese Patent Publication No. 57-48054, Unexamined Japanese Patent Publication No. 59-44457
The contents have already been published in various other areas. (For example, “OFFSHORE
GOTEBORG'81”Paper No.42Goteborg
SWEDEN1981, “Cement Concrete” No.
434 (1983) P.23/31, “Corrosion of Reinforcement in Concrete Construction”
Concrete Construction)” P419 1983, “Architectural Technical Execution” 1985, No. 229, January issue P155/164,
Shokokusha). In addition, the salt resistance mechanism of the steel components of reinforcing bars at an early stage, which contributes to improving the salt resistance of reinforcing bars themselves, is also described in detail in these published papers. (Problem to be solved by the invention) The present invention is based on the conventional development by the inventors,
Completely stop the corrosion deterioration of steel structures, automobiles, and other transportation equipment in the marine environment, coastal areas, and highways sprayed with antifreeze agents, which have recently become a particular problem, as well as the deterioration of concrete structures with buried steel materials. There is a particular thing. Among these, I would like to focus on prevention of salt damage deterioration of concrete, which has recently become a problem. The present invention focuses on the development of conventional salt-resistant concrete reinforcing bars, and the present invention focuses on reinforcing bars made of salt that exists in a free Cl ^- state such as sea salt particles and seawater splashes that penetrate concrete walls, which has recently become a particular problem. The purpose is to prevent corrosion of concrete and the accompanying cracking and deterioration of concrete. Currently, free salt near the buried reinforcing bars of concrete structures that are more than 10 years old, which is a problem in various fields, can reach up to 1.0% in terms of NaCl in the harsh marine environment, leading to severe corrosion of the reinforcing bars and resulting cracks in the concrete. , causing growth. Therefore, it is desirable to completely stop the corrosion of the buried reinforcing steel bars even with such high concentrations of salt, and to stop the occurrence of cracks in the concrete. (Means for Solving the Problems) The above objects of the present invention are achieved by providing a steel having the following structure. (1) C: 1.0% or less, Si: 0.25% or less, Mn: 2.0%
Below, Al: 7.0 to 20.0%, P: 0.015% or less,
S; 0.005% or less, Cr; 0.1 to 5.5% and Ce,
Rare earth elements such as La and Y are used singly or in combination.
Seawater resistant steel containing 0.01-0.5%, with the balance consisting of iron and unavoidable impurities. (2) C: 1.0% or less, Si: 0.25% or less, Mn: 2.0%
Below, Al: 7.0 to 20.0%, P: 0.015% or less,
S; 0.005% or less, Cr; 0.1 to 5.5% and Ce,
Rare earth elements such as La and Y are used singly or in combination.
Contains 0.01 to 0.5%, and further contains Ti, V, Nb, W,
One or two of Co, Mo, and B, with a total of 0.01 to 0.5% for elements other than B, and 0.0001 to 0.005% for B.
Seawater-resistant steel with the remainder iron and unavoidable impurities. (3) C: 1.0% or less, Si: 0.25% or less, Mn: 2.0%
Below, Al: 7.0 to 20.0%, P: 0.015% or less,
S; 0.005% or less, Cr; 0.1 to 5.5% and Ce,
Rare earth elements such as La and Y are used singly or in combination.
A seawater-resistant steel containing 0.01 to 0.5%, and further containing 0.1 to 5.5% of one or both of Cu and Ni, with the balance being iron and inevitable impurities. (4) C: 1.0% or less, Si: 0.25% or less, Mn: 2.0%
Below, Al: 7.0 to 20.0%, P: 0.015% or less,
S; 0.005% or less, Cr; 0.1 to 5.5% and Ce,
Rare earth elements such as La and Y are used singly or in combination.
Contains 0.01 to 0.5%, and further contains Ti, V, Nb, W,
One or two of Co, Mo, and B, with a total of 0.01 to 0.5% for elements other than B, and 0.0001 to 0.005% for B.
Contains 0.1 to 0.1 or more of one or both of Cu and Ni.
Seawater resistant steel containing 5.5%, with the remainder consisting of iron and unavoidable impurities. The greatest feature of the present invention is that Al content in the steel is 7.0 to 20.0.
%, and further contains a large amount of Cr (0.1 to 5.5%) to form a strong passive film in environments exposed to high concentrations of salt, almost eliminating rusting, and improving the quality of steel. The goal is to completely stop corrosion. Furthermore, even if the concrete in which these steels are buried is exposed to high concentrations of salt, the buried reinforcing steel in the concrete forms a strong passive film, which almost eliminates rusting and completely prevents concrete deterioration. It's about letting people know. That is, the idea is not to suppress the growth of rust as in conventional inventions, but to eliminate or suppress the generation of rust even in the presence of high concentrations of salt as described above. The cause of this is currently under investigation and is not clear, but it is believed that Al ³⁺ melted from the alloy of the present invention.
AlCl ₃ produced by reacting with Cl ^- reacts with OH ^- in water and immediately changes to extremely stable Al(OH) ₃ .
It is presumed that this is due to growth and blocking of corrosion factors. The reasons for limiting each component in the present invention will be explained below. The reason for limiting the C content to 1.0% or less is that the C content is 1.0%.
This is because exceeding this value causes embrittlement. or,
The reason why the Mn content is limited to 2.0% or less is that exceeding 2.0% causes embrittlement, so the preferred range is
It is 0.8% or less. The reason why the amount of Si was set to 0.25% or less is
This is because if the amount of Si exceeds 0.25%, graphitization of cementite in the steel is significantly promoted and workability deteriorates. In general, the lower the amount of Si, the less rust occurs, so a lower amount of Si is desirable.
The most desirable range is a Si content of less than 0.05%. Al is an important element that holds the key to the present invention, and is particularly effective in suppressing rust formation even at extremely high concentrations of salt. This effect cannot be expected if the Al content is less than 7.0%, and if it exceeds 20.0%, it may not only be economically disadvantageous but also cause embrittlement due to difficulty in controlling intermetallic compounds. The most preferable range is an Al content of 8.0% or more and 18% or less. The reason why P is set to be 0.015% or less is that P exceeding 0.015% has no effect of suppressing rust formation in an alkaline atmosphere such as concrete, but rather tends to accelerate it. The reason for setting the Cr content to 0.1% or more is that when the Al content is 7.0% or more, the seawater resistance improves dramatically, but when it exceeds 5.5%, it has been observed that embrittlement may occur. The amount of Cr was set to 0.1 to 5.5%. The most preferred range is 2.0-3.0%. Also, the amount of S is 0.005
The reason for limiting it to % or less is the origin of rust.
The aim is to reduce the amount of MnS, and to reduce the amount of S, it is expected that the corrosion resistance will be improved by converting MnS into (Mn, Ca)S etc. using Ca or a Ca compound used as a desulfurizing agent. Moreover, it is common knowledge to carry out the above-mentioned operation in order to reduce the amount of S in steel. The main aim of adding rare earth elements such as Ce, La, Y, etc. singly or in combination is to significantly reduce the amount of S through desulfurization in the steel, but at the same time, even when the amount of Mn is high, remaining sulfides are converted to complete αMnS. It was added in the hope that it would avoid this and change its chemical properties into sulfides and oxysulfides containing rare earth elements, thereby improving salt resistance. The lower limit is the minimum necessary content, and the upper limit is defined to significantly change the properties of these compounds, and is in the range of 0.01 to 0.5%. At this time, in order to promote desulfurization, a Ca compound is added to the molten steel in advance or at the same time, so Ca often coexists at about 0.0002% or less. In addition, in the present invention, Ti, V,
Nb, W, Co, Mo, B, etc. are added as well-known elements to improve the strength and toughness of reinforcing bars, and one or two types are selected and added.
Addition amount of 0.01 to 0.5% in total for other elements, B
is added in an amount of 0.0001 to 0.005%, which is already generally well known for the above purpose. Since these additive elements often exhibit similar addition effects, the purpose can be achieved by adding them singly or usually in combination. Further, if necessary, 0.1 to 5.5% of one or both of Cu and Ni may be added to improve weather resistance before being buried in concrete. If necessary, for example, when free machinability is required for threaded reinforcing bars, 0.01 to 0.5% of Pb can be added. According to the present invention, the steel composed of the above chemical components is melted in a converter, electric furnace, etc., and then subjected to the steps of ingot making and blooming, or after continuous casting and rolling, as required. The wire is then subjected to heat treatment such as quenching, tempering, or normalizing, or heat treatment such as patenting, and is then drawn into wire and used. The final products are supplied in the form of steel pipes, H-shaped steel, steel sheet piles, reinforced steel bars, wires, steel plates, etc., and can be galvanized or coated with organic coatings as required. (Example) Example 1 Steel with the components listed in Table 1 was melted in a vacuum melting furnace, and after ingot formation and blooming, the composition and corrosion test results of hot-rolled steel and conventional steel were compared. Indicated. Width 25mm x length 60mm x from the center of the prepared steel plate
A specimen with a thickness of 2 mm was taken, and the surface was polished by mechanical grinding. On the other hand, artificial seawater was prepared as an environment to promote or reproduce the corrosion of steel in seashore areas and seawater in the laboratory. After that, the surface of the sample was ground as described above, the side and back surfaces were coated with silicone resin, and after degreasing and drying, an enameled wire was connected as shown in Fig. 1.
It was immersed together with the carbon fiber bundle in the above artificial seawater. That is, a carbon fiber bundle and a reinforcing bar specimen were connected with an enameled wire in this way, a battery was formed between the two materials, and the battery was maintained for 3 days to observe the state of rust on the steel surface. The results are shown in Table 1. The back and side surfaces of the specimen surface and the enameled wires that came into contact with the liquid were all sealed with silicone resin. FIG. 1 is an explanatory diagram of the above-mentioned corrosion test, in which a carbon fiber bundle and a specimen were immersed in artificial seawater 3 in a container 1, and both were connected with an enameled wire 4.
5 in the figure represents the surface condition of the conventional steel as a comparative example after the 3-day test, and the shaded area indicates that rust has developed. Next, in order to promote or reproduce the salt-induced corrosion of buried reinforcing bars in concrete, CaO, the main component of concrete, was dissolved in a 3.6% NaCl aqueous solution to prepare a Ca(OH) ₂ +NaCl aqueous solution with a pH of 12. . Thereafter, the surface of the specimen was ground as described above, and the side and back surfaces were coated with silicone resin. The specimen was degreased, dried, and immediately immersed in the above Ca(OH) ₂ +3.6% NaCl aqueous solution. 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. These results are shown in Table 1. Example 2 After grinding the surface of a hot rolled steel plate consisting of the ingredients shown in Table 1,
It was exposed to a seashore area for one year, and after exposure, it was pickled and the corrosion loss was determined to calculate the corrosion rate. In addition, hot-rolled reinforcing bars (9 mmφ) made of the ingredients shown in Table 1 were embedded in a concrete mortar made of sand containing 1.0% NaCl, Portland cement, water, and gravel, and after curing at room temperature for 28 days, they were exposed to a seashore area for 1 year. . The water-cement ratio of the concrete was 0.60, and the fog thickness was 2 cm. After one year of exposure, the concrete was crushed and the rusting status of the reinforcing bars was investigated. The results of these investigations are shown in Table 1. The results of Table 1 show that the steel of the present invention has a high concentration of salt in concrete of 1.0% in terms of NaCl in sand, and 3.6% in water.
It was clearly observed that no rust occurred even at high concentrations of %NaCl, and it was found that the deterioration of concrete caused by rust occurrence and rust growth could be completely stopped.

【table】

【table】

[Table] (Effects of the invention) The present invention is useful as a steel material and concrete steel material that is extremely effective in maintaining the durability of steel materials exposed to salt damage and concrete structures buried in steel materials, and is useful in the marine environment. It can be used in a wide range of applications in environments exposed to severe salt damage, such as road deicing agent spraying environments.

[Brief explanation of drawings]

FIGS. 1a and 1b are explanatory diagrams of a corrosion test in the present invention. 1... Container, 2... Carbon fiber bundle, 3... 0.1%
Ca(OH) ₂ aqueous solution of PH12 containing NaCl, 4...
Enameled wire, 5...Conventional ordinary steel specimen, 6...Example specimen of the present invention.

Claims (1)

[Claims] 1 C: 1.0% or less, Si: 0.25% or less, Mn: 2.0%
Below, Al; 7.0 to 20.0%, P; 0.015% or less, S;
0.005% or less, Cr; 0.1-5.5% and Ce, La, Y
Rare earth elements such as 0.01 to 0.5 alone or in combination
%, with the remainder consisting of iron and unavoidable impurities. 2 C: 1.0% or less, Si: 0.25% or less, Mn: 2.0%
Below, Al; 7.0 to 20.0%, P; 0.015% or less, S;
0.005% or less, Cr; 0.1-5.5% and Ce, La, Y
Rare earth elements such as 0.01 to 0.5 alone or in combination
%, and further contains Ti, V, Nb, W, Co, Mo,
One or two types of B, in total for elements other than B
Seawater-resistant steel containing 0.01 to 0.5%, B 0.0001 to 0.005%, and the balance consisting of iron and inevitable impurities. 3 C: 1.0% or less, Si: 0.25% or less, Mn: 2.0%
Below, Al; 7.0 to 20.0%, P; 0.015% or less, S;
0.005% or less, Cr; 0.1-5.5% and Ce, La, Y
Rare earth elements such as 0.01 to 0.5 alone or in combination
%, and further contains one or two of Cu and Ni from 0.1 to
Seawater resistant steel containing 5.5%, with the remainder consisting of iron and unavoidable impurities. 4 C: 1.0% or less, Si: 0.25% or less, Mn: 2.0%
Below, Al; 7.0 to 20.0%, P; 0.015% or less, S;
0.005% or less, Cr; 0.1-5.5% and Ce, La, Y
Rare earth elements such as 0.01 to 0.5 alone or in combination
%, and further contains Ti, V, Nb, W, Co, Mo,
One or two types of B, in total for elements other than B
A seawater-resistant steel containing 0.01 to 0.5% of B, 0.0001 to 0.005% of B, and 0.1 to 5.5% of one or both of Cu and Ni, with the balance being iron and inevitable impurities.