JPS62297434A - Nonmagnetic steel having resistance to sea-water corrosion - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] (Field of Industrial Application) The present invention is applicable to steel structures and concrete structures, especially magnetic levitation high-speed railways, nuclear fusion facilities, marine equipment, and structures where non-magnetism is desired. This relates to the non-magnetic steel materials used.

That is, the purpose of the present invention is to provide a steel material suitable for the above-mentioned uses, and since the steel material itself has good corrosion resistance, it can also be used as a non-ferrous material that is useful for preventing deterioration of structures installed in oceans and coastal areas. This relates to magnetic steel materials.

(Prior Art) Recently, various prevention methods have been proposed or put into practice to prevent deterioration of steel structures and concrete structures installed in oceans and coastal areas.

The biggest cause of deterioration of steel structures is corrosion caused by seawater itself,
This is due to corrosion caused by sea salt particles, etc., but the biggest cause of concrete deterioration is that salt penetrating through concrete walls corrodes the reinforcing bars embedded in the concrete.
Since its volume is approximately 2.2 times that of steel, it cannot withstand the expansion force and cracks occur in the concrete along the buried reinforcing bars.

If the crack exceeds 0.2 liters, external corrosion factors such as oxygen, salt, and carbon dioxide in the air will more easily penetrate through the crack into the vicinity of the buried reinforcing steel, further accelerating the corrosion of the steel and causing concrete damage. This will accelerate the carbonation of concrete and accelerate the deterioration of concrete.

Now, recently, as mentioned above, prototype steel materials containing 15% or more of Mn have been made for the purpose of non-magnetization.
One of the disadvantages of any steel material is that even the presence of even a small amount of salt causes a significant degree of rust formation, which is more likely than the current ordinary steel, and the rate of corrosion is high.

(Problems to be Solved by the Invention) The present invention focuses on the conventional development by the present inventors, and solves the problem of corrosion of non-magnetic steel structures in coastal areas, which has recently become a particular problem, and the problem of burying non-magnetic steel materials. The goal is to completely stop the deterioration of concrete structures.

Currently, thick salt accumulates in the rust layer on the surface of steel structures that are more than 20 years old, which is a problem in various fields, and the free salt near the buried steel in concrete structures is equivalent to NaCA in sand. In some cases, it has reached approximately 2.0%, causing significant corrosion of buried steel materials and associated cracking and growth in concrete. Therefore, it is desirable to be able to almost completely stop corrosion of steel structures and cracking of concrete even when exposed to extremely high concentrations of salt.

(Means for solving the problems) The above-mentioned object of the present invention is that C: 2.0%, Al: 0.25
% or less, Mn; more than 2.0 to 7.0%, A/; 19.
0-22.3%, Pio, 015%, Al0.005
% or less, and optionally contains Ti, V, Nb,
W, Co.

If one or more of Mo and B are used as an element other than B, 0.
01-0.5%, B is 0.0001-0.005%, C
u, Ni.

This is achieved by a seawater-resistant non-magnetic steel material containing 0.25% of one or more Cr, with the balance consisting of iron and unavoidable impurities.

The greatest feature of the present invention is that a relatively large amount of AI is added to reduce the amount of Si and S in the steel and to stabilize the non-magnetization, and in order to stabilize the non-magnetization, Mn is added The point is that a large amount was added.

The reason for this is that by lowering the amount of Si, the generation and growth of rust is suppressed.At the same time, as the amount of Sfi is lowered, the amount of MnS, which is the point at which corrosion occurs, is significantly reduced, thereby minimizing the deterioration of corrosion resistance. By making the amount relatively large, the passive film on the surface of the steel material with a relatively high Mn content is strengthened, and even if exposed to high concentration of salt, the passive film will not be destroyed and rust will not occur. It is assumed that.

The reasons for limiting each component in the present invention will be explained below.

The reason why the C content is limited to 2.0% or less is that Cl exceeding 2.0% causes embrittlement.

The reason why 5ili is set to 0.25% or less is that the lower the amount of Si, the more the amount of rust formation will be dramatically reduced, but it is necessary to add Si for the purpose of ensuring strength and controlling inclusions. It was set to 0.25% or less. A more preferable range is 0.05% or less of Si.

The reason why Mn1l is set to exceed 2.0% is that if it is less than 2.0%, the degree of demagnetization may not be large, and if it exceeds 7.0%, hot rolling becomes difficult.

The reason why P is set to be less than o, ois% is that P is 0.015%
This is because if it exceeds 100%, it will not have the effect of suppressing rust growth in an alkaline atmosphere such as concrete, but rather tends to promote it.

Al is the most important metal element among the chemical components of the steel of the present invention. The reason for limiting i to 19.0 to 22.3% is that less than 19.0% makes demagnetization unstable.
If it exceeds 3%, metal open compounds of AA and Fe are likely to be formed.
This is because it causes embrittlement of the steel and makes hot rolling impossible. Therefore, the ingredients were limited to the above range.

The reason why Si is limited to 0.005% or less is to reduce MnS il, which is the source of rust. The effect of improving corrosion resistance by changing to Ca) S, etc. can also be expected. Also, Sfi in steel
It is common knowledge that the above operations are carried out to reduce the corrosion resistance, so a small amount of Ca, Ce, etc. may be mixed in, but these elements do not have a negative effect on corrosion resistance. Therefore, the presence of small amounts of Ca, Ce, etc. is not a problem.

In addition, in the present invention, Ti, V, N
b.

W, Co, Mo, B, etc. are added as well-known elements to improve the strength and toughness of steel.
0.01 to 0.5 for one or more elements other than B
% and B are added in an amount of 0.0001 to 0.005%, which is already generally well known for the above purpose.

Additionally, if necessary, Cu, Ni, Cr may be added to improve weather resistance.
Add 0.25% of one or more of the following.

Note that 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-mentioned chemical components is melted in a converter, electric furnace, etc., and then subjected to the process of ingot making or blooming, or after being continuously cast and rolled, it is baked if necessary. It is subjected to heat treatment such as hardening, 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-beams, steel sheet piles, reinforced steel bars, wires, tliI plates, etc., and can be galvanized or coated with an organic coating if necessary.

(Example) Example 1 Steel with the components listed in Table 1 was melted in a vacuum melting furnace, and ingot 2
The composition and corrosion test results of hot-rolled steel and conventional steel steel after blooming are shown.

A specimen measuring 25 mm wide x 60 mm long x 21 m thick was taken from the center of the prepared steel plate, 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.

Thereafter, the surface of the specimen was ground as described above, the side and back surfaces were coated with silicone resin, and the specimen was degreased, dried, and immediately immersed in the artificial seawater described above. This artificial seawater solution was changed every 7 days and was continuously immersed for 50 days, and the occurrence of rust was observed.

Next, in order to promote or reproduce the salt-induced corrosion of buried reinforcing bars in concrete, CaO, which is the main component of concrete, was dissolved in a 3.6% NaCl aqueous solution.
A Ca(OH)z + NaCl aqueous solution of H12 was prepared.

Thereafter, the surface of the sample was ground as described above and the side and back surfaces were coated with silicone resin. After degreasing and drying, the sample was immediately immersed in the above Ca(OH) z + 3.6% 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 immersed continuously for 20 days.
The state of rust formation was observed. These results are shown in Table 1.

Example 2 After grinding the surface of a hot-rolled steel plate made of the ingredients shown in Table 1, it was exposed to a beach area for one year, and the state of rusting was investigated.

In addition, hot-rolled reinforcing bars (9 1φ) made of the ingredients shown in Table 1 were embedded in a concrete mortar made of sand containing 2.0% NaCl, Portland cement, water, and gravel, and after curing at room temperature for 28 days, they were placed in a seaside area. Exposure was for 1 year.

The water-cement ratio of the concrete was 0.60, and the fog thickness was 2c1n.

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 in Table 1 show that the rope of the present invention does not cause any leakage even in seawater, and the salt in the concrete is as low as NaCj in the sand! 2.0 in conversion
It was clearly observed that no rust occurred even at a high concentration of 3.6% NaCl in water, and it was found that rust generation and deterioration of concrete due to rust growth could be completely prevented. Therefore, it is presumed that the deterioration of both steel structures and concrete structures can be completely suppressed even in extremely harsh marine environments.

(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 non-magnetic steel materials exposed to salt damage and concrete structures in which non-magnetic steel materials are buried. It can be used in a wide range of applications that require non-magnetic properties, such as magnetic levitation railways exposed to salt damage, such as coastal areas.

Successive correction (self-motivated) July 8, 1986 Commissioner of the Patent Office Kuro 1) Akio 1. Display of incident 1985 Patent Application No. 105809 2. Name of the invention Seawater resistant non-magnetic steel material 3. Person who makes corrections Relationship to the incident: Patent applicant 2-6-3 Otemachi, Chiyoda-ku, Tokyo (665) Nippon Steel Corporation Representative Takeshi 1) Yutaka 4. Agent〒100 2-4-1 Marunouchi, Chiyoda-ku, Tokyo (1) Insert the following between lines 4 and 5 on page N6 of the details.

``In addition, C becomes magnetic due to heat treatment etc. (Fe, A/
) 3C composite carbide? Since it is easy to generate, the lower the amount of C, the better. The preferred range is C gold 0.001 to 0.
It is 1%. (2) 11Ca (○H) in the third column from the right of Table 1 on page 11
) 2 + In the rusting area (%) column after immersion in 36% NaCl aqueous solution, the value r1oo of conventional steel, corner 1, + is set to "42", the value of thread 2 is "100", and "4.3 J, A3 The value of “100
Correct J to "51".

Claims (4)

[Claims] (1) C: 1.0% or less, Si: 0.25% or less, Mn
; more than 2.0 to 7.0%, Al; 19.0 to 22.3%,
A seawater-resistant non-magnetic steel material containing P: 0.015% or less, S: 0.005% or less, with the balance consisting of iron and unavoidable impurities. (2) C: 1.0% or less, Si: 0.25% or less, Mn
; more than 2.0 to 7.0%, Al; 19.0 to 22.3%,
Contains P: 0.015% or less, S: 0.005% or less, and further contains one or more of Ti, V, Nb, W, Co, Mo, and B as an element other than B: 0.01 to 0 .5%, B;
A seawater-resistant nonmagnetic steel material containing 0.0001 to 0.005%, with the remainder consisting of iron and inevitable impurities. (3) C: 1.0% or less, Si: 0.25% or less, Mn
; more than 2.0 to 7.0%, Al; 19.0 to 22.3%,
A seawater-resistant nonmagnetic steel material containing P: 0.015% or less, S: 0.005% or less, and consisting of Cu, the balance iron, and inevitable impurities. (4) C: 1.0% or less, Si: 0.25% or less, Mn
; more than 2.0 to 7.0%, Al; 19.0 to 22.3%,
Contains P: 0.015% or less, S: 0.005% or less, and one or more of Ti, V, Nb, W, Co, Mo, and B and an element other than B: 0.01 to 0. 5%, B; 0.0
001 to 0.005%, and further contains Cu, Ni, Cr
A seawater-resistant nonmagnetic steel material containing 0.1 to 5.5% of one or more of the following, with the balance being iron and inevitable impurities.