JPH02138441A - Seawater resistant steel with improved rust resistance - 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] (Industrial Application Field) The present invention is applicable to steel structures and concrete structures, especially those installed in marine environments, beach areas, and environments where road antifreeze is sprayed. , and further relates to steel used in harsh saline environments in transportation equipment such as automobiles and vehicles that run in these environments.

That is, the purpose of the present invention is to provide a rope 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 and NaCZ.

This product relates to seawater-resistant steel that is useful for preventing deterioration of transportation equipment such as automobiles that travel on expressways that are sprayed with road antifreeze agents such as Ca01.

(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 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.

When the crack is 0.2 am or more, external corrosion factors such as oxygen, salt, and carbon dioxide gas in the air can more easily penetrate into the vicinity of the buried reinforcing steel inside the steel through the crack, further promoting the corrosion of scrap metal. This will promote the carbonation of concrete and hasten the deterioration of concrete.

In addition, in winter, on expressways where road antifreeze has been sprayed, the concentrated salt causes rapid deterioration of not only the roads, but also the cars traveling on these roads due to corrosion, and various prevention methods are used to prevent this deterioration. However, this has not completely stopped the deterioration.

Now, among these, salt damage deterioration of concrete has recently received a lot of attention, so 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. 57-4805
4, Japanese Patent Application Laid-Open No. 59-44457).
These contents have already been published in various other areas. (
For example, “0FFSIIORII!GOTEBORG
'81'' Paper Na 42 Gotebor
g 5WEDEN19B, 1 year, “Cement Concrete” N11434 (1983) P, 23/31.
“Corrosion of Reinforcement in Concrete Construction”
ion of Reinforcement i
n Concrete(：□y13jruction
)”P, 4191983, II Architecture Technical Construction” 1
985, k229 January issue P, 155/164. 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 of the present inventors, and is based on the steel structures used in the marine environment, seashore areas, and highways where road antifreeze is sprayed, which has recently become a particular problem. The goal is to completely stop the corrosion and deterioration of transportation equipment such as cars and vehicles, as well as the deterioration of concrete structures with buried steel materials. 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.Reinforcing bars made of salt that exists in a free C1- state, such as sea salt particles and seawater splashes that penetrate concrete walls, have 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 160% in terms of NaC1 in the harsh marine environment, causing 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: 0.1% or less, St: 0.25% or less, Mn
; 1.0% or less, AZ; 5.8 to less than 7.0%, P
; 0.015% or less, S, 0.005% or less, Cr
; more than 1.5 to 7.0% and rare earth elements such as Ce, La, Y, etc., alone or in combination, 0.001 to 0.5
%, the remainder consists of iron and unavoidable impurities, and the seawater-resistant steel has improved rust resistance, characterized in that Al≧Cr.

(2) C: 0.1% or less, St: 0.25% or less, Mn
; 1.0% or less, /V; 5.8 to less than 7.0%, P
; 0.015% or less, S, O, 005% or less, C
r; more than 1.5 to 7.0% and Ce, l, a,
Rare earth elements such as Y alone or in combination from 0.001 to 0
．． Contains 5% of Ti and V.

One or two of Nb, W, Co, Mo, B,
For elements other than B, the total is 0. O1-0.5%, B 0.
A seawater-resistant steel with improved rust resistance, characterized by containing 0001 to 0.005%, the remainder consisting of iron and unavoidable impurities, and satisfying Al≧Cr.

(3) C: 0.1% or less, St: 0.25% or less, Mn
; 1.0% or less, Aj i 0.8 to less than 7.0%, P
; 0.015% or less, S i O, 005% or less, Cr
more than 1.5 to 7.0% and 0.001 to 0.5% of rare earth elements such as Ce, La, and Y, singly or in combination, and further contains 0.001 to 0.5% of one or both of Cu and Ni. 1-5
．． Contains 5%, the balance consists of iron and inevitable impurities,
A seawater-resistant steel with improved rust resistance, characterized in that Al≧Cr.

(4) C; 0.1% or less, Si; 0.25% or less, Mn
; 1, 0% or less, Aj; 5.8 to less than 7.0%, P
; 0.015% or less, S i O, 005% or less, Cr
>1.5 to 7.0% and rare earth elements such as Ce, La, Y, etc. alone or in combination 0.001 to 0.5%
Contains Ti, V.

One or two of Nb, W, Co, Mo, B,
The total content of elements other than B is 0.01 to 0.5%, and B is 0.
0001 to 0.005%, further containing 0.1 to 5.5% of one or both of Cu and Ni, the balance being iron and inevitable impurities, and Al≧Cr. Seawater resistant steel with improved rust resistance.

The biggest feature of this invention is in steel! 548-7.0%
In addition, Cr is contained in a large amount such that All≧Cr4J
By containing a large amount of over 1.5 to 7.0% while maintaining the relationship between 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 the AlCl3 produced by the reaction of M''3 melted from the alloy according to the present invention with 01-
reacts with O1+- in water and immediately produces extremely stable Aj.
(0) changes to 3, which is presumed to grow and block corrosion factors.

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

The reason why the amount of C is limited to 0.1% or less is that if Cl exceeds 0.1%, embrittlement will occur. Also, Mn hare 1
．． The reason why it is limited to 0% or less is that if it exceeds 1.0%, it causes embrittlement, and the preferable range is 0.8% or less. The reason for setting sin to 0.25% or less is that the amount of Si is 0.25% or less.
This is because if it exceeds 25%, graphitization of cementite in the steel is significantly promoted and workability deteriorates. Generally S
The lower the i content, the less rust occurs, so Si
A lower amount is preferable. The most desirable range is 5ifi0
．． Less than 0.05%.

M is an important element that holds the key to the present invention, and has the effect of suppressing rust even at extremely high concentrations of salt. This effect cannot be expected when Alff is less than 16.8%, and when it is over 7.0%. Not only is this economically disadvantageous, but it may also become brittle due to difficulty in controlling intermetallic compounds.

The most preferable range is Alff of 16.0% or more and less than 7.0%.

The reason why P is set to be 0.015% or less is that if it exceeds 0.015%, it has no effect of suppressing rust formation in an alkaline atmosphere such as concrete, but rather tends to promote it.

The reason why the Cr content is set to be more than 1.5% is that when the IV content is less than 7.0%, rust resistance in a seawater environment is dramatically improved when the IV content is coexisting. If the Cr content exceeds .0%, embrittlement was observed in some cases, so the Cr content was set to more than 1.5% to 7.0%. The most preferred range is 3.0-6.0
% range. The relationship between N content and Crl in steel is Al≧Cr
The reason for this is that when the Cr content is within the above range and this relationship is established, long-term rust resistance of the steel plate sprayed in seawater is recognized. Also, Si is 0. The reason for limiting it to 0.005% or less is to reduce MnS lil, which is the source of rust, and to reduce s4, MnS (Mn,
The effect of improving corrosion resistance by changing to Ca)S etc. can also be expected. Further, it is common knowledge to carry out the above-mentioned operation in order to lower the sl in steel.

The main aim of adding rare earth elements such as Ce, La, Y, etc. individually or in combination is to significantly reduce Sl by desulfurization in steel, but at the same time, even when Mnfl is high, the remaining sulfide becomes complete αMnS. It was added in the hope that it would change into sulfides and oxysulfides containing rare earth elements, change their chemical properties, and improve 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 0.001 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 is often present in an amount of about 0.0002% or less.

In addition, in the present invention, Ti, V, Nb may be added as necessary.
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, and elements other than B are added in total. Addition amount of 0.01 to 0.5%, B is 0.0001
The amount of addition is set at ~o.oos%, but the above purpose is already generally well known. Since these additive elements often exhibit similar addition effects, the purpose can be achieved by adding them singly or usually in combination.

In addition, if necessary, one or both of Cu and Ni may be added in an amount of 0.1 to 0.1 to improve weather resistance before being buried in concrete.
Add 5.5%.

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 composition can be produced in a converter,
It is melted in an electric furnace, etc., and then goes through the steps of ingot making and blooming, or after being continuously cast and rolled, it is subjected to heat treatment such as quenching, tempering, or skewering as necessary.
It is subjected to heat treatment such as patenting, drawn, and ready for use. The final products include steel pipes, H-shaped steel, steel sheet piles,
It is supplied in the form of reinforced steel bars, wires, steel plates, etc., and can be galvanized or coated with organic coatings as required.

(Example) Example 1 Table 1 shows the chemical composition and corrosion test of steel materials of the present invention obtained by melting in a vacuum melting furnace, ingot making, blooming, and hot rolling, and steel materials made of conventional steel. The results were shown.

A specimen measuring 25 m wide x 60 m long x 2 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.

After that, the surface was ground as described above, and the side and back surfaces were coated with silicone resin. After degreasing and drying, JrSZ
A salt spray test was conducted using No. 2371, and the rusted area was measured after 10 hours. The results are shown in Table 1.

From the results in Table 1, it can be seen that while the conventional steel had 100% rusting, the steels of the present invention had no rusting.

Therefore, it was clearly demonstrated that the steel of the present invention is dramatically superior to conventional steel in terms of rust resistance.

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% Na (J) aqueous solution.
H12 Ca(011)z+Na1J aqueous solution is fJA
Prepared.

Thereafter, the surface of the specimen was ground as described above, the sides and back were coated with a silicone oven, the specimen was degreased, dried, and 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, 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 having the components shown in Table 1, it was exposed to a seaside area for one year, and after the exposure, it was pickled, and the corrosion loss was determined and the corrosion rate was calculated.

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 placed in a seaside area for one year. exposed.

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.

From the results in Table 1, the steel of the present invention has a high concentration of salt in concrete of 1.0% in terms of NaC1 during crushing, and 3.6%N in water.
It was clearly observed that even at a high concentration of aC1, there was no rust formation, and it was found that the deterioration of concrete caused by rust formation and rust growth could be completely stopped.

(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 and frozen roads. It can be used in a wide range of applications in environments exposed to severe salt damage, such as in environments where inhibitors are being sprayed.

Claims (4)

[Claims] (1) C: 0.1% or less, Si: 0.25% or less, Mn
; 1.0% or less, Al; 5.8 to less than 7.0%, P; 0
．． 015% or less, S; 0.005% or less, Cr; 1.5
Contains ultra-7.0% and 0.001 to 0.5% of rare earth elements such as Ce, La, Y, etc. singly or in combination, the balance consists of iron and inevitable impurities, and Al≧Cr. Seawater resistant steel with improved rust resistance. (2) C; 0.1% or less, Si; 0.25% or less, Mn
; 1.0% or less, Al; 5.8 to less than 7.0%, P; 0
．． 015% or less, S; 0.005% or less, Cr; 1.5
Contains ultra-7.0% and 0.001 to 0.5% of rare earth elements such as Ce, La, and Y, singly or in combination, and further contains one of Ti, V, Nb, W, Co, Mo, and B. Or two types, 0.01 to 0.5% in total for elements other than B, B is 0
．． A seawater-resistant steel with improved rust resistance, characterized in that it contains 0001 to 0.005%, the balance is iron and unavoidable impurities, and that M≧Cr. (3) C; 0.1% or less, Si; 0.25% or less, Mn
; 1.0% or less, Al; 5.8 to less than 7.0%, P; 0
．． 015% or less, S; 0.005% or less, Cr; 1.5
It contains 0.001 to 0.5% of rare earth elements such as Ce, La, Y, etc. alone or in combination, and further contains 0.1 to 5.0% of one or both of Cu and Ni. Contains 5%,
The balance consists of iron and inevitable impurities, and Al≧Cr
Seawater resistant steel with improved rust resistance. (4) C; 0.1% or less, Si; 0.25% or less, Mn
; 1.0% or less, M; 5.8 to less than 7.0%, P; 0.
Contains 0.015% or less, S: 0.005% or less, Cr: more than 1.5 to 7.0%, and 0.001 to 0.5% of rare earth elements such as Ce, La, and Y, singly or in combination, Further T
One or two of i, V, Nb, W, Co, Mo, B,
The total content of elements other than B is 0.01 to 0.5%, and B is 0.
0001 to 0.005%, and further contains 1 of Cu and Ni.
1. A seawater-resistant steel with improved rust resistance, containing 0.1 to 5.5% of one or two species, the remainder consisting of iron and unavoidable impurities, and satisfying Al≧Cr.